Ok-Guru

aws

2024-02-28T02:29:00.000-08:00

IAM

Amazon Identity and Access Management (IAM) is a web service offered by Amazon Web Services (AWS) that enables you to securely control access to AWS services and resources. IAM allows you to manage users, groups, roles, and their permissions in a flexible and fine-grained manner. Here are the key components and concepts of IAM:

Users:

IAM users represent individual people, services, or applications that interact with AWS resources.

Each user has a unique username and security credentials (access key ID and secret access key) to make programmatic calls to AWS services.

Example:

Creating a new user named "JohnDoe" with programmatic access.

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aws iam create-user --user-name JohnDoe

Groups:

Groups are collections of IAM users. You can attach policies to groups, and all users in the group inherit those policies.

This helps in managing permissions at scale, especially when multiple users need similar access rights.

Example:

Creating a group named "Developers" and adding the user "JohnDoe" to it.

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aws iam create-group --group-name Developers

aws iam add-user-to-group --group-name Developers --user-name JohnDoe

Roles:

IAM roles are similar to users, but they are not associated with a specific person. Instead, they are assumed by entities such as AWS services, EC2 instances, or applications.

Roles define a set of permissions that determine what actions can be performed on which AWS resources.

Example:

Creating a role named "S3ReadOnlyRole" with permissions to read objects from an S3 bucket.

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aws iam create-role --role-name S3ReadOnlyRole --assume-role-policy-document file://trust-policy.json

Contents of trust-policy.json:

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{

"Version": "2012-10-17",

"Statement": [

{

"Effect": "Allow",

"Principal": {

"Service": "ec2.amazonaws.com"

"Action": "sts:AssumeRole"

}

]

}

Policies:

IAM policies are JSON documents that define permissions. Policies can be attached to users, groups, or roles.

Policies specify the actions allowed or denied on resources and the conditions under which those actions are allowed or denied.

Example:

Attaching a policy to a group to grant read-only access to an S3 bucket.

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aws iam attach-group-policy --policy-arn arn:aws:iam::aws:policy/AmazonS3ReadOnlyAccess --group-name Developers

Access Control Lists (ACLs) and Bucket Policies:

Apart from IAM policies, S3 buckets have their own access control mechanisms, including ACLs and bucket policies.

ACLs and bucket policies define who can access objects within a bucket and under what conditions.

Example:

Configuring an S3 bucket policy to allow public read access to all objects.

json

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{

"Version": "2012-10-17",

"Statement": [

{

"Effect": "Allow",

"Principal": "*",

"Action": "s3:GetObject",

"Resource": "arn:aws:s3:::your-bucket-name/*"

}

]

}

These are just basic examples to illustrate the concepts. In practice, IAM is a powerful and flexible system that allows you to manage access to AWS resources in a granular way, ensuring security and compliance for your applications and services.

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Amazon Elastic Compute Cloud (Amazon EC2) is a web service provided by Amazon Web Services (AWS) that allows users to rent virtual servers in the cloud. EC2 instances provide scalable computing capacity and can be configured with various specifications to meet different application requirements. Here are the key aspects of Amazon EC2:

Instances:

EC2 instances are virtual servers that run on physical hardware within AWS's data centers.

Users can choose from a wide range of instance types with varying CPU, memory, storage, and networking capacities.

Examples of instance types include t2.micro, m5.large, c5.xlarge, etc.

Example:

Launching an EC2 instance using the AWS Management Console:

Amazon Machine Images (AMIs):

AMIs are pre-configured templates that contain the necessary information to launch an instance, including the operating system, application server, and applications.

Users can use public AMIs provided by AWS, create their own custom AMIs, or use AMIs shared by the community.

Example:

Creating a custom AMI based on an existing EC2 instance.

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aws ec2 create-image --instance-id i-1234567890abcdef0 --name "My server" --description "An AMI for my server"

Key Pairs:

EC2 instances use key pairs for secure login. When an instance is launched, users specify a key pair, and the corresponding private key is used to authenticate and log in to the instance.

Windows instances use a password instead of key pairs.

Example:

Creating a key pair using the AWS CLI:

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aws ec2 create-key-pair --key-name MyKeyPair

Security Groups:

Security groups act as virtual firewalls for EC2 instances, controlling inbound and outbound traffic.

Users can define rules for allowing or denying specific types of traffic to and from instances.

Example:

Creating a security group allowing SSH (port 22) and HTTP (port 80) traffic.

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aws ec2 create-security-group --group-name MySecurityGroup --description "My security group"

aws ec2 authorize-security-group-ingress --group-name MySecurityGroup --protocol tcp --port 22 --cidr 0.0.0.0/0

aws ec2 authorize-security-group-ingress --group-name MySecurityGroup --protocol tcp --port 80 --cidr 0.0.0.0/0

Elastic Load Balancing:

Elastic Load Balancing (ELB) distributes incoming application traffic across multiple EC2 instances to ensure no single instance is overwhelmed.

ELB improves the availability and fault tolerance of applications.

Example:

Creating an Application Load Balancer using the AWS CLI.

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aws elbv2 create-load-balancer --name MyLoadBalancer --subnets subnet-0123456789abcdef0 subnet-0123456789abcdef1 --security-groups sg-0123456789abcdef0

Auto Scaling:

Auto Scaling allows users to automatically adjust the number of EC2 instances in a group based on demand or a defined schedule.

It helps ensure that the desired number of instances are running to handle the application load.

Example:

Creating an Auto Scaling group to maintain a desired capacity of EC2 instances.

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aws autoscaling create-auto-scaling-group --auto-scaling-group-name MyAutoScalingGroup --launch-configuration-name MyLaunchConfig --min-size 2 --max-size 5 --desired-capacity 3 --vpc-zone-identifier subnet-0123456789abcdef0 subnet-0123456789abcdef1

Storage Options:

EC2 instances can use various types of storage, including Amazon Elastic Block Store (EBS) volumes and instance store volumes.

EBS volumes provide persistent block-level storage, while instance store volumes are temporary storage associated with the EC2 instance.

Example:

Creating an EBS volume and attaching it to an EC2 instance.

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aws ec2 create-volume --availability-zone us-east-1a --size 50

aws ec2 attach-volume --volume-id vol-049df61146d4d7901 --instance-id i-0c3d6f99bbEXAMPLE --device /dev/sdf

These are just some of the key features and concepts related to Amazon EC2. EC2 provides a flexible and scalable infrastructure for running virtual servers in the cloud, making it a foundational service for many applications and workloads on AWS.

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Amazon Simple Storage Service (Amazon S3) is a scalable object storage service provided by Amazon Web Services (AWS). It is designed to store and retrieve any amount of data from anywhere on the web. Here are the key aspects of Amazon S3:

Objects and Buckets:

In S3, data is organized into containers called "buckets." Buckets are like top-level directories and must have a globally unique name within S3.

Within each bucket, data is stored as objects. An object consists of data, a key (unique within the bucket), and metadata.

Example:

Creating an S3 bucket using the AWS Management Console:

Storage Classes:

Amazon S3 offers different storage classes to meet various performance and cost requirements. These include Standard, Intelligent-Tiering, Standard-IA (Infrequent Access), One Zone-IA, Glacier (for archival), and Glacier Deep Archive.

Users can choose the appropriate storage class based on the access frequency and durability requirements of their data.

Example:

Setting the storage class of an object to "Intelligent-Tiering" using the AWS CLI:

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aws s3 cp my-file.txt s3://my-bucket/ --storage-class INTELLIGENT_TIERING

Data Transfer Acceleration:

S3 Transfer Acceleration uses the CloudFront global content delivery network to accelerate uploading and downloading of objects to and from S3.

It is especially useful for large-scale data transfers or when accessing S3 from locations far from the AWS region where the bucket is stored.

Example:

Enabling Transfer Acceleration for an S3 bucket using the AWS CLI:

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aws s3api put-bucket-accelerate-configuration --bucket my-bucket --accelerate-configuration Status=Enabled

Versioning:

S3 provides versioning, allowing users to preserve, retrieve, and restore every version of every object stored in a bucket.

Versioning helps protect against accidental deletion or overwriting of objects.

Example:

Enabling versioning for an S3 bucket using the AWS Management Console:

Access Control and Permissions:

S3 allows users to control access to their buckets and objects using bucket policies, Access Control Lists (ACLs), and Identity and Access Management (IAM) policies.

Fine-grained access permissions can be defined based on factors such as the requester's identity, IP address, or time of day.

Example:

Configuring a bucket policy to grant public read access to all objects in the bucket:

json

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{

"Version": "2012-10-17",

"Statement": [

{

"Effect": "Allow",

"Principal": "*",

"Action": "s3:GetObject",

"Resource": "arn:aws:s3:::my-bucket/*"

}

]

}

Events and Triggers:

S3 supports event notifications, allowing users to trigger actions (such as invoking AWS Lambda functions or SQS messages) when specific events occur in their buckets.

Events include object creation, deletion, and restoration.

Example:

Configuring an S3 bucket to send a notification to an SNS topic when a new object is created:

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aws s3api put-bucket-notification-configuration --bucket my-bucket --notification-configuration file://notification-config.json

Contents of notification-config.json:

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{

"TopicConfigurations": [

{

"Id": "s3-object-created",

"TopicArn": "arn:aws:sns:us-east-1:123456789012:my-sns-topic",

"Events": ["s3:ObjectCreated:*"]

}

]

}

Data Lifecycle Management:

S3 provides features for managing the lifecycle of objects, including transitioning objects between storage classes, setting expiration policies, and automatically deleting objects after a specified period.

Example:

Configuring a lifecycle policy to transition objects to the "Glacier" storage class after 30 days:

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{

"Rules": [

{

"Status": "Enabled",

"Prefix": "",

"Transitions": [

{

"Days": 30,

"StorageClass": "GLACIER"

}

]

}

]

}

Amazon S3 is a highly durable and available object storage service that is widely used for various purposes, including data backup, archival, data lakes, and serving static assets for web applications. Its simple and scalable architecture makes it a fundamental component of many cloud-based solutions.

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Certainly! Amazon Virtual Private Cloud (VPC) is a service provided by Amazon Web Services (AWS) that allows you to create a logically isolated section of the AWS Cloud where you can launch resources in a virtual network that you define. When setting up a VPC, you often structure it with public and private subnets, along with route tables, gateways, and Network Address Translation (NAT) devices. Let's break down each component:

VPC (Virtual Private Cloud):

A VPC is the fundamental building block of your network in AWS. It allows you to provision a logically isolated section of the AWS Cloud where you can launch AWS resources.

You have control over your VPC's IP address range, subnets, route tables, and network gateways.

Subnets:

Subnets are subdivisions of your VPC's IP address range. You can create public and private subnets based on your needs.

Public Subnet: Typically used for resources that need to be directly accessible from the internet, such as web servers. It has a route to the internet.

Private Subnet: Used for resources that should not be directly accessible from the internet, such as databases or application servers. It does not have a route to the internet.

Route Tables:

A route table contains a set of rules, called routes, that are used to determine where network traffic is directed.

Each subnet in your VPC must be associated with a route table. This controls the traffic leaving the subnet.

Internet Gateway:

An Internet Gateway (IGW) is a horizontally scaled, redundant, and highly available VPC component that allows communication between instances in your VPC and the internet.

Typically, a public subnet is associated with an Internet Gateway to enable direct internet access for resources within that subnet.

NAT Gateway or NAT Instance:

NAT allows instances in a private subnet to initiate outbound traffic to the internet while preventing inbound traffic from initiating a connection with those instances.

There are two types of NAT:

NAT Gateway: A managed AWS service that provides better availability and automatically scales based on your needs.

NAT Instance: A manually configured EC2 instance that you set up as a NAT device.

Here's a simplified flow:

Instances in the public subnet can communicate directly with the internet via the Internet Gateway.

Instances in the private subnet can initiate outbound connections to the internet using a NAT Gateway or NAT Instance, but they don't accept incoming connections initiated from the internet.

This architecture provides security by restricting direct internet access to resources in the private subnet while allowing necessary communication for resources in the public subnet.

Certainly! Let's expand on the previous explanation and include an Application Load Balancer (ALB) in the architecture:

Amazon Virtual Private Cloud (VPC):

A VPC is a logically isolated section of the AWS Cloud where you can launch AWS resources. It provides you with control over your network environment, including IP address range, subnets, route tables, and gateways.

Subnets:

Subnets are divisions of your VPC's IP address range. You can create public and private subnets to organize your resources.

Public Subnet: Typically used for resources that need to be directly accessible from the internet, such as web servers. It has a route to the internet.

Private Subnet: Used for resources that should not be directly accessible from the internet, such as databases or application servers. It does not have a route to the internet.

Route Tables:

A route table contains a set of rules, or routes, that are used to determine where network traffic is directed.

Each subnet in your VPC must be associated with a route table. This controls the traffic leaving the subnet.

Internet Gateway (IGW):

An Internet Gateway is a horizontally scaled, redundant component that allows communication between instances in your VPC and the internet.

Typically, a public subnet is associated with an Internet Gateway to enable direct internet access for resources within that subnet.

Network Address Translation (NAT):

NAT allows instances in a private subnet to initiate outbound traffic to the internet while preventing inbound traffic initiated from the internet.

Two types of NAT:

NAT Gateway: A managed AWS service that provides better availability and scales automatically.

NAT Instance: A manually configured EC2 instance that serves as a NAT device.

Application Load Balancer (ALB):

An Application Load Balancer is a service that automatically distributes incoming application traffic across multiple targets, such as EC2 instances, in one or more availability zones.

ALB operates at the application layer, making it well-suited for applications that require flexibility in routing requests.

Typically, the ALB is placed in the public subnet to distribute incoming web traffic to instances in the private subnet.

Flow of Traffic:

Public Subnet:

Instances in the public subnet, such as web servers, can communicate directly with the internet via the associated Internet Gateway.

An Application Load Balancer in the public subnet receives incoming traffic from the internet and distributes it to the backend instances.

Private Subnet:

Instances in the private subnet do not have direct internet access.

Outbound traffic from instances in the private subnet is routed through a NAT Gateway or NAT Instance to reach the internet.

This architecture ensures that resources in the private subnet are protected from direct internet exposure, while still allowing them to communicate with the internet for necessary updates and external services through the NAT gateway or NAT instance. The ALB in the public subnet handles incoming web traffic and distributes it to the appropriate instances in the private subnet.

I can describe the architecture visually, but I can't draw diagrams directly. However, I can provide you with a text-based representation of the architecture. You can use this as a guide to create a diagram using drawing tools or on paper.

Explanation:

The VPC encompasses the entire architecture.
Within the VPC, there are two subnets: a public subnet and a private subnet.
The public subnet contains an Internet Gateway (IGW) and an Application Load Balancer (ALB).
The private subnet contains a NAT Gateway for outbound internet access and instances that need to be protected from direct internet exposure.

Arrows indicating the flow of traffic might be added between components as needed. Remember to adapt this representation based on your specific IP addressing, availability zones, and any additional components or services you may have in your architecture.

How to debug application performance issues

2024-02-21T06:28:00.000-08:00

Diagnosing and debugging performance issues in applications can involve various steps and tools. Here's a general guide on how to check and debug low application performance:

Monitor Resources:

Use monitoring tools like AWS CloudWatch, Prometheus, or other application performance monitoring (APM) tools to track metrics such as CPU usage, memory utilization, disk I/O, and network activity.

Identify any resource bottlenecks that could be affecting performance.

Review Logs:

Check application logs for error messages, warnings, or any unusual behavior.

Utilize logging services like CloudWatch Logs, ELK Stack (Elasticsearch, Logstash, Kibana), or centralized logging systems to aggregate and analyze logs.

Profiling:

Use profiling tools to analyze the runtime behavior of your application. Tools like AWS X-Ray, New Relic, or YourKit can help identify performance bottlenecks in code.

Profiling helps pinpoint areas of the code that consume the most resources or time.

Database Performance:

Examine database queries and their execution times. Use database monitoring tools to identify slow queries.

Optimize database indexes and query structures for better performance.

Network Latency:

Check for network issues using tools like traceroute or ping to identify latency or packet loss.

Utilize distributed tracing tools to analyze network interactions within microservices.

Caching and Content Delivery:

Implement caching mechanisms to reduce the load on backend systems.

Use Content Delivery Networks (CDNs) to distribute static content and improve response times.

Load Testing:

Conduct load tests to simulate various user scenarios and identify how the application performs under different levels of load.

Tools like Apache JMeter or locust can be used for load testing.

Code Review:

Review the application code for performance bottlenecks, inefficient algorithms, or suboptimal database queries.

Consider code profiling and optimization techniques.

Infrastructure Scaling:

Evaluate if the application infrastructure (e.g., EC2 instances, containers) is appropriately sized. Consider scaling horizontally or vertically based on requirements.

Utilize auto-scaling features to dynamically adjust resources based on demand.

Security Considerations:

Ensure that security measures, such as firewalls and authentication mechanisms, are not causing unnecessary overhead.

Audit for security vulnerabilities that might impact performance.

Browser Performance:

Analyze frontend performance using browser developer tools to identify slow-loading resources, excessive DOM manipulations, or rendering issues.

Continuous Monitoring:

Implement continuous monitoring and alerting to receive notifications when performance metrics deviate from normal ranges.

Establish baseline performance metrics for comparison.

Python string

2023-10-10T07:24:00.002-07:00

Python provides a wide range of built-in functions and methods for working with strings. Here is a list of some commonly used string functions and methods:

len(): Returns the length of the string.

python

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s = "Hello, World!"

length = len(s) # length is 13

str(): Converts a value to a string.

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num = 42

s = str(num) # s is "42"

concatenation: Combining strings using the + operator.

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s1 = "Hello"

s2 = "World"

s3 = s1 + ", " + s2 # s3 is "Hello, World"

format(): Format a string using placeholders.

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name = "Alice"

age = 30

s = "My name is {} and I am {} years old.".format(name, age)

f-strings (formatted string literals): A more concise way to format strings using f-strings (Python 3.6+).

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name = "Alice"

age = 30

s = f"My name is {name} and I am {age} years old."

strip(): Removes leading and trailing whitespace.

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s = " Hello, World! "

s = s.strip() # s is now "Hello, World!"

split(): Splits a string into a list based on a delimiter.

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s = "apple,banana,cherry"

fruits = s.split(",") # fruits is ["apple", "banana", "cherry"]

join(): Joins a list of strings into a single string using a delimiter.

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fruits = ["apple", "banana", "cherry"]

s = ",".join(fruits) # s is "apple,banana,cherry"

find(): Searches for a substring and returns its index or -1 if not found.

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s = "Hello, World!"

index = s.find("World") # index is 7

replace(): Replaces all occurrences of a substring with another string.

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s = "Hello, World!"

new_s = s.replace("World", "Python") # new_s is "Hello, Python!"

upper(): Converts all characters to uppercase.

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s = "Hello, World!"

upper_s = s.upper() # upper_s is "HELLO, WORLD!"

lower(): Converts all characters to lowercase.

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s = "Hello, World!"

lower_s = s.lower() # lower_s is "hello, world!"

startswith() and endswith(): Checks if a string starts or ends with a specified substring.

python

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s = "Hello, World!"

starts_with = s.startswith("Hello") # True

ends_with = s.endswith("World") # True

count(): Counts the number of occurrences of a substring in a string.

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s = "Hello, World!"

count = s.count("l") # count is 3

isalpha(), isdigit(), isalnum(): Check if the string consists of alphabetic characters, digits, or alphanumeric characters.

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s1 = "Hello"

s2 = "123"

s3 = "Hello123"

is_alpha = s1.isalpha() # True

is_digit = s2.isdigit() # True

is_alnum = s3.isalnum() # True

isupper() and islower(): Check if all characters in the string are uppercase or lowercase, respectively.

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s1 = "HELLO"

s2 = "world"

is_upper = s1.isupper() # True

is_lower = s2.islower() # True

capitalize(): Converts the first character of the string to uppercase and the rest to lowercase.

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s = "hello world"

capitalized_s = s.capitalize() # "Hello world"

title(): Converts the first character of each word in the string to uppercase.

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s = "hello world"

title_s = s.title() # "Hello World"

swapcase(): Swaps the case of all characters in the string.

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s = "Hello, World!"

swapped_s = s.swapcase() # "hELLO, wORLD!"

isnumeric() and isdecimal(): Check if all characters in the string are numeric or decimal digits, respectively.

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s1 = "12345"

s2 = "12.34"

is_numeric = s1.isnumeric() # True

is_decimal = s2.isdecimal() # False

isprintable(): Check if all characters in the string are printable (e.g., not control characters).

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s = "Hello, World!"

is_printable = s.isprintable() # True

zfill(): Pads the string with zeros on the left until it reaches a specified width.

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s = "42"

padded_s = s.zfill(5) # "00042"

rjust() and ljust(): Right-justifies or left-justifies the string within a specified width, padding with a specified character.

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s = "42"

rjust_s = s.rjust(5, "0") # "00042"

ljust_s = s.ljust(5, "0") # "42000"

center(): Centers the string within a specified width, padding with a specified character.

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s = "42"

centered_s = s.center(5, "0") # "00420"

encode(): Encodes the string into bytes using a specified encoding.

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s = "Hello, World!"

encoded_bytes = s.encode("utf-8")

startswith() and endswith(): Check if a string starts or ends with a specified substring.

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s = "Hello, World!"

starts_with = s.startswith("Hello") # True

ends_with = s.endswith("World") # True

commonly asked python string interview questions with answer

ChatGPT

Certainly! Here are some commonly asked Python string interview questions along with their answers:

Reverse a String:

Q: Write a Python function to reverse a string.

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def reverse_string(input_str):

return input_str[::-1]

Check for Palindrome:

Q: Write a Python function to check if a string is a palindrome.

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def is_palindrome(input_str):

return input_str == input_str[::-1]

Count Occurrences:

Q: Write a Python function to count the occurrences of a substring in a given string.

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def count_substring_occurrences(input_str, substring):

return input_str.count(substring)

Anagram Detection:

Q: Write a Python function to check if two strings are anagrams of each other.

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def are_anagrams(str1, str2):

return sorted(str1) == sorted(str2)

String Compression:

Q: Write a Python function to perform basic string compression using the counts of repeated characters.

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def compress_string(input_str):

compressed = ""

count = 1

for i in range(1, len(input_str)):

if input_str[i] == input_str[i - 1]:

count += 1

else:

compressed += input_str[i - 1] + str(count)

count = 1

compressed += input_str[-1] + str(count)

return compressed if len(compressed) < len(input_str) else input_str

String Rotation:

Q: Write a Python function to check if one string is a rotation of another.

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def is_rotation(str1, str2):

if len(str1) != len(str2):

return False

return str2 in (str1 + str1)

Longest Common Prefix:

Q: Write a Python function to find the longest common prefix of a list of strings.

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def longest_common_prefix(strs):

if not strs:

return ""

common_prefix = min(strs)

for i, char in enumerate(common_prefix):

for string in strs:

if string[i] != char:

return common_prefix[:i]

return common_prefix

String to Integer (atoi):

Q: Implement the atoi function, which converts a string to an integer.

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def atoi(s):

s = s.strip()

if not s:

return 0

sign = -1 if s[0] == '-' else 1

if s[0] in ('-', '+'):

s = s[1:]

result = 0

for char in s:

if not char.isdigit():

break

result = result * 10 + int(char)

return max(min(result * sign, 2**31 - 1), -2**31)

These are some common Python string interview questions and their corresponding answers. These questions cover a range of string manipulation techniques and can help you prepare for interviews that involve string manipulation in Python.

Certainly! Here are some more tricky Python string interview questions along with their answers:

First Non-Repeating Character: Q: Write a Python function to find the first non-repeating character in a string.

python
def first_non_repeating_char(s):
    char_count = {}
    for char in s:
        char_count[char] = char_count.get(char, 0) + 1
    for char in s:
        if char_count[char] == 1:
            return char
    return None

Valid Parentheses: Q: Write a Python function to check if a given string containing parentheses is valid.

python
def is_valid_parentheses(s):
    stack = []
    brackets = {')': '(', '}': '{', ']': '['}
    for char in s:
        if char in brackets.values():
            stack.append(char)
        elif char in brackets.keys():
            if not stack or stack.pop() != brackets[char]:
                return False
        else:
            return False
    return not stack

Longest Substring Without Repeating Characters: Q: Write a Python function to find the length of the longest substring without repeating characters.

python
def length_of_longest_substring(s):
    char_index = {}
    max_length = start = 0
    for i, char in enumerate(s):
        if char in char_index and char_index[char] >= start:
            start = char_index[char] + 1
        char_index[char] = i
        max_length = max(max_length, i - start + 1)
    return max_length

String Permutations: Q: Write a Python function to generate all permutations of a given string.

python
from itertools import permutations

def string_permutations(s):
    return [''.join(p) for p in permutations(s)]

Implement strStr(): Q: Implement the strStr() function, which finds the index of the first occurrence of a substring in another string.

python
def strStr(haystack, needle):
    if not needle:
        return 0
    for i in range(len(haystack) - len(needle) + 1):
        if haystack[i:i+len(needle)] == needle:
            return i
    return -1

Group Anagrams: Q: Given a list of strings, group anagrams together.

python
from collections import defaultdict

def group_anagrams(strs):
    grouped = defaultdict(list)
    for s in strs:
        key = ''.join(sorted(s))
        grouped[key].append(s)
    return list(grouped.values())

Decode String: Q: Given an encoded string, return its decoded string.

python
def decode_string(s):
    stack = []
    curr_num = 0
    curr_str = ""
    for char in s:
        if char.isdigit():
            curr_num = curr_num * 10 + int(char)
        elif char == '[':
            stack.append((curr_str, curr_num))
            curr_str, curr_num = "", 0
        elif char == ']':
            prev_str, num = stack.pop()
            curr_str = prev_str + curr_str * num
        else:
            curr_str += char
    return curr_str

These tricky Python string interview questions cover more advanced string manipulation techniques and problem-solving skills. They are designed to challenge your understanding of strings and algorithms.

Certainly! Here are some more challenging Python string interview questions along with their answers:

Valid Palindrome II: Q: Given a non-empty string s, you may delete at most one character. Write a Python function to check if you can make it a palindrome.

python
def valid_palindrome(s):
    def is_palindrome(s, left, right):
        while left < right:
            if s[left] != s[right]:
                return False
            left += 1
            right -= 1
        return True

    left, right = 0, len(s) - 1
    while left < right:
        if s[left] != s[right]:
            return is_palindrome(s, left + 1, right) or is_palindrome(s, left, right - 1)
        left += 1
        right -= 1
    return True

Minimum Window Substring: Q: Given two strings S and T, find the minimum window in S that will contain all the characters in T.

python
def min_window_substring(s, t):
    from collections import Counter

    t_counter = Counter(t)
    required_chars = len(t)
    left = right = 0
    min_len = float('inf')
    min_window = ""

    while right < len(s):
        if s[right] in t_counter:
            if t_counter[s[right]] > 0:
                required_chars -= 1
            t_counter[s[right]] -= 1

        while required_chars == 0:
            if right - left + 1 < min_len:
                min_len = right - left + 1
                min_window = s[left:right + 1]

            if s[left] in t_counter:
                t_counter[s[left]] += 1
                if t_counter[s[left]] > 0:
                    required_chars += 1
            left += 1

        right += 1

    return min_window

Regular Expression Matching: Q: Implement regular expression matching with support for '.' and '*'.

python
def is_match(s, p):
    if not p:
        return not s
    first_match = bool(s) and (s[0] == p[0] or p[0] == '.')

    if len(p) >= 2 and p[1] == '*':
        return (is_match(s, p[2:]) or (first_match and is_match(s[1:], p)))
    else:
        return first_match and is_match(s[1:], p[1:])

Longest Substring with At Most K Distinct Characters: Q: Given a string s and an integer k, return the length of the longest substring with at most k distinct characters.

python
def length_of_longest_substring_k_distinct(s, k):
    from collections import defaultdict

    max_length = 0
    left = 0
    char_count = defaultdict(int)

    for right in range(len(s)):
        char_count[s[right]] += 1

        while len(char_count) > k:
            char_count[s[left]] -= 1
            if char_count[s[left]] == 0:
                del char_count[s[left]]
            left += 1

        max_length = max(max_length, right - left + 1)

    return max_length

These advanced Python string interview questions require a deeper understanding of string manipulation, algorithms, and problem-solving skills. They are designed to challenge your ability to tackle complex string-related problems.

Certainly! Here are more Python string interview questions:

Valid Number: Q: Write a Python function to determine if a given string is a valid number (integer or floating-point).

python
def is_valid_number(s):
    try:
        float(s)
        return True
    except ValueError:
        return False

Reverse Words in a String: Q: Write a Python function to reverse the words in a string while preserving the order of words.

python
def reverse_words(s):
    words = s.split()
    reversed_str = ' '.join(reversed(words))
    return reversed_str

Longest Substring Without Repeating Characters (with k distinct characters): Q: Modify the previous "Longest Substring with At Most K Distinct Characters" question to return the actual substring itself.

python
def longest_substring_k_distinct(s, k):
    from collections import defaultdict

    max_length = 0
    left = 0
    char_count = defaultdict(int)
    start_index = 0

    for right in range(len(s)):
        char_count[s[right]] += 1

        while len(char_count) > k:
            char_count[s[left]] -= 1
            if char_count[s[left]] == 0:
                del char_count[s[left]]
            left += 1

        if right - left + 1 > max_length:
            max_length = right - left + 1
            start_index = left

    return s[start_index:start_index + max_length]

Add Binary Strings: Q: Given two binary strings, return their sum (also a binary string).

python
def add_binary(a, b):
    carry = 0
    result = []
    i, j = len(a) - 1, len(b) - 1

    while i >= 0 or j >= 0 or carry:
        sum = carry
        if i >= 0:
            sum += int(a[i])
            i -= 1
        if j >= 0:
            sum += int(b[j])
            j -= 1

        carry = sum // 2
        result.append(str(sum % 2))

    return ''.join(result[::-1])

Longest Palindromic Substring: Q: Find the longest palindromic substring in a given string.

python
def longest_palindromic_substring(s):
    def expand_around_center(left, right):
        while left >= 0 and right < len(s) and s[left] == s[right]:
            left -= 1
            right += 1
        return s[left + 1:right]

    longest = ""
    for i in range(len(s)):
        # Odd length palindrome
        palindrome1 = expand_around_center(i, i)
        if len(palindrome1) > len(longest):
            longest = palindrome1

        # Even length palindrome
        palindrome2 = expand_around_center(i, i + 1)
        if len(palindrome2) > len(longest):
            longest = palindrome2

    return longest

These additional Python string interview questions will further test your problem-solving skills and ability to work with strings in various scenarios.

String Reversal Without Built-in Functions: Q: Write a Python function to reverse a string without using any built-in string reversal functions (e.g., slicing).

python
def reverse_string(input_str):
    reversed_str = ""
    for char in input_str:
        reversed_str = char + reversed_str
    return reversed_str

Check for Anagrams: Q: Write a Python function to check if two strings are anagrams of each other without using any built-in sorting functions.

python
def are_anagrams(str1, str2):
    if len(str1) != len(str2):
        return False
    
    char_count = {}
    
    for char in str1:
        if char in char_count:
            char_count[char] += 1
        else:
            char_count[char] = 1

    for char in str2:
        if char in char_count:
            char_count[char] -= 1
            if char_count[char] < 0:
                return False
        else:
            return False
    
    return True

Count Vowels and Consonants: Q: Write a Python function to count the number of vowels and consonants in a given string.

python
def count_vowels_and_consonants(input_str):
    vowels = "aeiouAEIOU"
    vowel_count = 0
    consonant_count = 0
    
    for char in input_str:
        if char.isalpha():
            if char in vowels:
                vowel_count += 1
            else:
                consonant_count += 1
    
    return vowel_count, consonant_count

Check for Pangram: Q: Write a Python function to check if a given string is a pangram (contains every letter of the alphabet at least once).

python
def is_pangram(input_str):
    alphabet = "abcdefghijklmnopqrstuvwxyz"
    return all(char in input_str.lower() for char in alphabet)

String Compression: Q: Write a Python function to perform basic string compression by replacing consecutive repeating characters with the character followed by the count.

python
def compress_string(input_str):
    compressed = ""
    count = 1
    for i in range(1, len(input_str)):
        if input_str[i] == input_str[i - 1]:
            count += 1
        else:
            compressed += input_str[i - 1] + str(count)
            count = 1
    compressed += input_str[-1] + str(count)
    return compressed if len(compressed) < len(input_str) else input_str

These simple yet tricky Python string interview questions are designed to test your understanding of string manipulation techniques and problem-solving skills with a twist.

All in One QA interview questions with answer - SDET

2023-10-10T00:32:00.003-07:00

Write a program for explaining a singleton class.

A singleton class is a design pattern in object-oriented programming that ensures a class has only one instance and provides a global point of access to that instance. It is commonly used when you want to restrict the instantiation of a class to a single object and control access to that object across your program. Singleton classes are often used for managing resources, configurations, or instances that should be shared across multiple parts of an application.

Here's a Python program that demonstrates the implementation of a singleton class:

class Singleton:

_instance = None # Private class variable to store the single instance

def __new__(cls):

if cls._instance is None:

cls._instance = super(Singleton, cls).__new__(cls)

cls._instance.value = None # Initialize an attribute (can be any data)

return cls._instance

# Usage of the Singleton class

instance1 = Singleton()

instance1.value = "First Instance Value"

instance2 = Singleton()

instance2.value = "Second Instance Value"

# Both instances refer to the same object

print("Instance 1:", instance1.value) # Output: "Second Instance Value"

print("Instance 2:", instance2.value) # Output: "Second Instance Value"

In this example:

The `Singleton` class defines a private class variable `_instance` that will store the single instance of the class.
The `__new__` method is overridden to control the creation of instances. It checks whether the `_instance` variable is `None`. If it is, it creates a new instance and assigns it to _instance. If `_instance` is not `None,` it returns the existing instance.
When you create instances of the `Singleton` class (e.g., `instance1` and `instance2`), both will refer to the same object, even if you try to modify their attributes. This behavior ensures that only one instance of the class exists throughout the program.

Using a singleton class, you can ensure that there is a single point of access to shared resources or configurations, and you can prevent multiple instantiations of the same class, which might be useful in scenarios like database connections, logging, or managing global application settings.

Scenario when singleton is used in python

Singletons are used in Python when you want to ensure that a particular class has only one instance throughout the lifetime of your application. They are often used in scenarios where you need to manage shared resources, configuration settings, or coordinate tasks across the program. Here are some common scenarios in which you might use a singleton in Python:

Database Connections: When working with databases, you often want to maintain a single database connection that can be shared across different parts of your application. Using a singleton pattern ensures that you create only one instance of the database connection class, saving resources and preventing connection-related issues.
Logging: In a logging system, you might want to have a single logger instance that can be accessed by various modules or components to log events and messages consistently. A singleton can ensure that all parts of your application use the same logger instance.
Configuration Management: If your application relies on configuration settings or parameters, you can use a singleton to read and manage these settings from a central configuration file or source. This ensures that all parts of your codebase access the same configuration data.
Caching: When implementing a caching mechanism, a singleton cache manager can help you maintain a single cache across your application. This can be useful for caching frequently accessed data to improve performance.
Resource Managers: In scenarios where you need to manage limited resources, such as threads, connections, or hardware devices, a singleton pattern can help ensure that these resources are efficiently shared and allocated.
Application State: For certain applications, you might want to maintain a global state that multiple components can access and modify. A singleton can serve as a central repository for storing and managing application state.
Global Service Instances: In larger applications, you might have services such as authentication, messaging, or file management that need to be accessible from different parts of the codebase. A singleton pattern ensures that these services are globally accessible and maintain a single instance.
Plugin Systems: In some cases, you might implement a plugin system where plugins or extensions need access to a common interface or manager. A singleton can provide a single point of access to register and manage plugins.

Remember that while singletons can be helpful in managing shared resources and global state, they should be used judiciously. Overusing singletons can lead to tightly coupled code and make unit testing more challenging. Therefore, it's essential to carefully consider whether a singleton pattern is the most appropriate solution for your specific use case.

When we do not use Singleton Design pattern

While singleton design pattern has its use cases, there are scenarios where it may not be the best choice, and other design patterns or approaches may be more suitable. Here are situations where using a singleton is generally not recommended:

When Multiple Instances Are Necessary: The primary purpose of a singleton is to ensure that only one instance of a class exists. If your application genuinely requires multiple instances of a class, using a singleton pattern would be counterproductive. In such cases, you should use regular class instantiation.
Testing and Mocking: Singleton classes can make unit testing more challenging because they introduce global state. If you need to isolate components for testing or replace a real object with a mock or stub, singletons can interfere with these practices. It's often preferable to use dependency injection or other patterns that facilitate testability.
Resource Cleanup: In scenarios where you need to manage resource cleanup explicitly, singletons can be problematic. Since they persist throughout the application's lifetime, it can be challenging to release resources when they are no longer needed. Resource management may be better handled through other patterns or mechanisms.
Immutable State: If the state of an object should remain immutable, using a singleton is not appropriate. Singletons typically allow for state modifications, which may lead to unintended changes in multiple parts of your program.
Dynamic Object Creation: If you need to create objects dynamically based on specific conditions or parameters, a singleton pattern is not well-suited. Singleton classes are instantiated only once during the program's lifetime, so they don't support dynamic object creation.
Global Variables: While singletons can provide a controlled way to manage global state, excessive use of global variables, including singleton instances, can lead to code that is hard to understand, debug, and maintain. It's generally advisable to minimize global state where possible.
Concurrency and Thread Safety: Singleton patterns do not inherently address issues related to concurrency and thread safety. If your application involves multithreading or multiprocessing, you may need to implement additional synchronization mechanisms to ensure safe access to the singleton instance. In some cases, alternative patterns like the "Borg" pattern or dependency injection may be more suitable for managing shared resources in a thread-safe manner.
Inflexibility: Using a singleton can introduce inflexibility into your codebase. If you anticipate the need to replace or extend the functionality of a class with different implementations, a more flexible design pattern, such as the Factory Method or Dependency Injection, may be more appropriate.

In conclusion, the decision to use or not use a singleton pattern should be based on a careful assessment of your specific application requirements. While singletons can be beneficial in certain scenarios, they should not be applied universally, and other design patterns and architectural approaches should be considered when they better align with your project's needs.

AWS VPC

2023-10-02T12:06:00.000-07:00

What is an AWS VPC, and why is it important for cloud infrastructure?
Answer: An AWS Virtual Private Cloud (VPC) is a virtual network dedicated to an AWS account. It allows you to provision and isolate resources in the cloud. VPCs are essential for security and network control in the cloud, enabling you to create private networks, control IP address ranges, and define network access.

Explain the difference between a public subnet and a private subnet in an AWS VPC.
Answer: In a VPC, a public subnet is one that has a route to the internet via an Internet Gateway, typically used for resources like web servers. A private subnet, on the other hand, lacks a direct route to the internet and is used for resources that should not be directly accessible from the internet, such as databases or application servers.

How do you create a custom VPC in AWS, and what are the essential components of a VPC?
Answer: You can create a custom VPC through the AWS Management Console, AWS CLI, or using CloudFormation templates. Essential VPC components include subnets, route tables, security groups, network ACLs, and an optional VPN connection or Direct Connect gateway for on-premises connectivity.

What is CIDR notation, and how is it used when defining IP address ranges in a VPC?
Answer: CIDR (Classless Inter-Domain Routing) notation is a way to represent IP address ranges and their subnet masks. When defining IP address ranges in a VPC, you specify the CIDR block for the VPC and subnets, e.g., 10.0.0.0/16 for the VPC and 10.0.1.0/24 for a subnet.

Can you describe the purpose and use cases of a Network Access Control List (NACL) in a VPC?
Answer: A Network Access Control List (NACL) acts as a stateless firewall for controlling inbound and outbound traffic at the subnet level in a VPC. It is used for security and filtering traffic, and common use cases include controlling access to resources, blocking malicious traffic, and segmenting network traffic within a VPC.

What is a Security Group in AWS, and how does it differ from a NACL?
Answer: A Security Group acts as a stateful firewall for controlling inbound and outbound traffic at the instance level, while a NACL operates at the subnet level and is stateless. Security Groups are more specific to instances and are rule-based, whereas NACLs are less granular and work with subnets.

How can you connect an on-premises network to an AWS VPC? What are the different methods available for this?
Answer: You can connect an on-premises network to an AWS VPC using AWS Direct Connect, VPN (Virtual Private Network) connections, or AWS Transit Gateway, depending on the requirements of your hybrid network architecture.

Explain the concept of Elastic IP (EIP) in AWS. Why might you use EIPs in a VPC?
Answer: An Elastic IP (EIP) is a static, public IPv4 address that you can allocate to your AWS resources. EIPs are used to ensure that the public IP address of an EC2 instance or a NAT gateway remains constant, even if the instance is stopped and started. They are often used to host public-facing applications or services.

What are the considerations when designing a multi-region VPC architecture?
Answer: Designing a multi-region VPC architecture involves several considerations:

Data Replication: Decide how data will be replicated across regions to ensure high availability and disaster recovery.
Latency: Consider network latency between regions and optimize routing for performance.
Security: Implement consistent security policies across regions, considering compliance requirements.
DNS: Set up DNS resolution and naming conventions for cross-region resources.
Traffic Engineering: Use AWS Global Accelerator or Route 53 for traffic distribution.
Cost: Plan for data transfer costs between regions and optimize resource usage.

How would you perform VPC backups and disaster recovery planning for a critical application?
Answer: VPC backups and disaster recovery planning for a critical application involve:

Snapshotting EBS volumes: Regularly create snapshots of critical data volumes for point-in-time backups.
Cross-region replication: Use services like AWS S3 cross-region replication for data redundancy.
Multi-AZ deployments: Deploy instances and databases across multiple Availability Zones (AZs) for high availability.
Automated backups: Implement automated backup policies for databases and other stateful services.
Disaster recovery runbooks: Document recovery procedures, including failover strategies and resource restoration processes.

Can you explain the concept of VPC Flow Logs and how they can be used for security and troubleshooting?
Answer: VPC Flow Logs capture network traffic metadata (e.g., source/destination IP, ports, protocol) and can be used for security and troubleshooting purposes:

Security: Analyze Flow Logs to detect and investigate suspicious traffic patterns or potential security breaches.
Troubleshooting: Identify network connectivity issues, diagnose performance problems, and audit network behavior.
Compliance: Use Flow Logs to meet compliance and auditing requirements by tracking network traffic history.

What are the limitations or constraints of AWS VPC, and how would you work around them in specific scenarios?

Answer: AWS VPC has some limitations that may affect design choices:

IP Address Range: VPCs have size limitations (e.g., /16 to /28), so plan IP ranges carefully and consider VPC peering if needed.
Route Tables: VPCs have a limit on the number of route tables, so use them efficiently and consider Transit Gateway for large-scale designs.
NAT Gateways: Limited scalability per Availability Zone, so use NAT instances or Transit Gateway for high-traffic scenarios.
Direct Connect: Limited redundancy options, so implement backup connections or use AWS VPN for additional redundancy.
Elastic Network Interfaces: Limited number per instance type, so consider instance type when designing highly networked applications.

Describe a real-world scenario where you faced a challenging problem related to AWS VPC and how you resolved it.

Answer: In my previous role, we encountered a challenge where a critical application hosted in a VPC was experiencing intermittent connectivity issues. After thorough investigation and Flow Log analysis, we discovered that our security group rules were overly restrictive, causing legitimate traffic to be dropped. We revised the security group rules, implemented better logging, and established a more robust monitoring solution to proactively detect and address similar issues in the future.

You have a VPC with multiple subnets, both public and private. Instances in the private subnets need to access the internet for updates, but you want to minimize exposure. How can you achieve this?

Answer: You can set up a NAT Gateway in a public subnet and configure the private subnets' route tables to route outbound traffic through the NAT Gateway. This allows instances in private subnets to access the internet while minimizing their exposure to inbound traffic from the internet.

Explain the implications of a VPC's default security group.

Answer: The default security group allows all inbound traffic from other instances assigned to the same security group but denies all inbound traffic from instances in other security groups or the internet. It also allows all outbound traffic. This can be tricky because sometimes users expect it to behave like a traditional firewall, but it's more permissive by default.

You have a VPC with two private subnets and want to ensure high availability for your EC2 instances. What strategy would you use?

Answer: To ensure high availability, you can distribute your EC2 instances across multiple Availability Zones (AZs) within the private subnets. You can also use an Auto Scaling group with an appropriate desired capacity to automatically recover instances in case of failure.

What is the purpose of a VPC Peering Connection, and what limitations should you be aware of when using it?

Answer: VPC Peering allows you to connect two VPCs to route traffic between them. However, you should be aware of some limitations, such as no transitive routing (you can't route through a VPC to reach another VPC), and overlapping CIDR blocks between peered VPCs are not allowed.

You need to securely connect your on-premises data center to your AWS VPC. How would you design a highly available, fault-tolerant solution?

Answer: You can design a highly available solution by using multiple Direct Connect connections or VPN tunnels over different physical paths and Availability Zones. Additionally, you can use Border Gateway Protocol (BGP) for dynamic routing and route failover.

What is a VPC Transit Gateway, and how does it simplify network architecture?

Answer: A VPC Transit Gateway is a service that simplifies network architecture by acting as a hub that connects multiple VPCs and on-premises networks. It reduces the need for complex VPC peering and simplifies routing. However, you should be aware of the routing limitations and data transfer costs associated with it.

How can you enforce encryption between instances in a VPC, even if developers do not configure it at the application level?

Answer: You can enforce encryption by using Network ACLs (NACLs) and Security Groups to restrict inbound and outbound traffic to use only secure protocols (e.g., HTTPS) and deny traffic that uses unencrypted protocols (e.g., HTTP).

You have an EC2 instance in a private subnet that needs to download software updates from the internet. How can you configure this without exposing the instance to the public internet?

Answer: You can configure a NAT Gateway or NAT Instance in a public subnet and then set up a route in the private subnet's route table to route all outbound traffic (0.0.0.0/0) through the NAT Gateway/Instance. This allows the private subnet's instances to access the internet for updates while remaining private.

What's the difference between a Network ACL (NACL) and a Security Group (SG) when controlling traffic to an EC2 instance?

Answer: NACLs are stateless and operate at the subnet level, whereas SGs are stateful and operate at the instance level. SGs are used to control inbound and outbound traffic to an EC2 instance, while NACLs are used to control traffic at the subnet level. This difference can be tricky because it impacts how you design security rules.

You have a VPC with multiple subnets, and you want to allow communication between some subnets while preventing communication between others. How can you achieve this?

Answer: You can use Security Groups and NACLs to control traffic between subnets. Create appropriate rules in Security Groups to allow or deny traffic between instances, and configure NACLs to control subnet-level traffic. By carefully configuring these security settings, you can achieve the desired communication patterns.

What is the purpose of a Bastion Host, and how can it be used to enhance security in a VPC?

Answer: A Bastion Host (or Jump Box) is used as a secure gateway to access instances in a private subnet. It enhances security by reducing the exposure of private instances to the internet. Users connect to the Bastion Host first and then use it as a gateway to access other private instances via SSH or RDP.

You have a VPC with two private subnets in different Availability Zones. How can you ensure high availability for your database, which needs to be accessible from both subnets?

Answer: To ensure high availability, you can deploy the database in an active-passive or multi-AZ configuration, with synchronous replication between AZs. Additionally, use DNS or a load balancer to direct traffic to the active instance. This setup ensures that the database remains accessible even if one AZ experiences a failure.

You need to limit the number of API requests to an internal service running on EC2 instances in a private subnet. How can you achieve rate limiting for API requests?

Answer: You can implement rate limiting by using a service like AWS API Gateway, which allows you to configure throttling settings to limit the number of requests per second or minute to your internal service. Alternatively, you can use a third-party API gateway or a custom solution like Nginx with rate limiting.

Question: What does VPC stand for, and what is its main purpose in AWS?

Answer: VPC stands for Virtual Private Cloud. Its main purpose is to create a private, isolated network environment within AWS, allowing users to launch and manage AWS resources securely.

Question: What is an IP address range in the context of a VPC?

Answer: An IP address range, specified in CIDR notation (e.g., 10.0.0.0/16), defines the range of private IP addresses available for use within a VPC.

Question: How are subnets used within a VPC, and why are they important?

Answer: Subnets are used to logically divide the IP address range of a VPC into smaller segments. They are associated with specific Availability Zones (AZs) and are important for organizing resources, implementing security, and improving fault tolerance.

Question: What is an Internet Gateway (IGW) in a VPC, and when is it used?

Answer: An Internet Gateway is a VPC component used to allow resources in public subnets to communicate with the internet. It is essential when resources, like web servers, need to be publicly accessible.

Question: What is the purpose of a Security Group (SG) in AWS VPC?

Answer: A Security Group acts as a virtual firewall for EC2 instances within a VPC. It controls inbound and outbound traffic to and from instances, allowing you to specify the rules for access.

Question: How does Network Access Control List (NACL) differ from a Security Group (SG) in AWS VPC?

Answer: NACLs are stateless, operate at the subnet level, and control traffic at a broader level compared to SGs, which are stateful, operate at the instance level, and provide more granular control over traffic.

Question: What is the purpose of a NAT Gateway (Network Address Translation) in AWS VPC?

Answer: A NAT Gateway is used to allow instances in private subnets to access the internet for software updates or external services while maintaining security. It acts as an intermediary for outbound traffic.

Question: Why might you need to create a VPC peering connection?

Answer: VPC peering connections are created to enable private communication between resources in different VPCs. This is useful when you want to share data or resources between VPCs while keeping them isolated from other networks.

Question: How can you connect your on-premises network to resources in a VPC?

Answer: You can connect your on-premises network to a VPC using either a VPN (Virtual Private Network) connection or AWS Direct Connect, depending on your network requirements and bandwidth needs.

Question: What is the significance of Availability Zones (AZs) in a VPC?

Answer: Availability Zones are physically separate data centers within an AWS region. Placing resources in different AZs provides redundancy and fault tolerance, ensuring that your applications remain available even if one AZ experiences issues.

1. Question: Explain the differences between a public subnet and a private subnet in a VPC.

Answer: In a VPC, a public subnet is associated with a route table that directs traffic to an Internet Gateway (IGW), allowing resources in the subnet to have direct internet access. In contrast, a private subnet is associated with a route table that does not have a route to the IGW, making resources in the subnet inaccessible from the public internet. Typically, application servers are placed in public subnets, while database servers are placed in private subnets to enhance security.

2. Question: Can you describe the role of Network Access Control Lists (NACLs) in a VPC? How do they differ from Security Groups (SGs)?

Answer: NACLs are stateless network-level firewalls that control traffic in and out of subnets within a VPC. They operate at the subnet level and provide rule-based filtering for IP traffic. Unlike SGs, which are stateful and operate at the instance level, NACLs apply to all resources in a subnet. NACLs are evaluated before SGs, and they can be used to create coarse-grained network traffic rules, while SGs provide fine-grained control at the instance level.

3. Question: What is the purpose of a Bastion Host (Jump Box) in a VPC, and how is it typically used?

Answer: A Bastion Host is a specially configured EC2 instance in a public subnet that serves as a secure gateway for administrators to access resources in private subnets. It enhances security by reducing the exposure of private instances to the internet. Administrators connect to the Bastion Host using SSH or RDP and then use it as a bridge to access other private instances within the VPC. This setup limits direct internet access to critical instances and provides a controlled access point for administrative tasks.

4. Question: How can you achieve high availability and fault tolerance for an application hosted in a VPC?

Answer: To achieve high availability and fault tolerance:

Deploy resources in multiple Availability Zones (AZs) within the same region to ensure redundancy.
Use Elastic Load Balancers (ELBs) to distribute traffic across instances in different AZs.
Set up Auto Scaling to automatically adjust the number of instances based on demand.
Implement database Multi-AZ deployments for database redundancy.
Configure DNS failover using Amazon Route 53 or a global accelerator for automatic failover between AZs in case of an outage.

5. Question: Explain the concept of VPC Peering and when you would use it.

Answer: VPC Peering allows the connection of two VPCs, enabling private communication between resources in those VPCs. It is typically used when you need to share resources or data securely between VPCs belonging to the same or different AWS accounts. VPC Peering is not transitive, meaning that if VPC A is peered with VPC B and VPC B is peered with VPC C, VPC A and VPC C are not automatically peered. You must establish direct peering connections between them if needed.

6. Question: Describe the differences between AWS Direct Connect and VPN when connecting on-premises networks to a VPC.

Answer: AWS Direct Connect is a dedicated network connection between an on-premises data center and AWS, providing consistent network performance and higher bandwidth. It's suitable for organizations with higher data transfer needs and stringent latency requirements. On the other hand, VPN (Virtual Private Network) connections use encrypted tunnels over the public internet and are suitable for smaller-scale connectivity requirements where the performance difference is acceptable.

7. Question: How can you secure sensitive data at rest and in transit within a VPC?

Answer: To secure sensitive data within a VPC:

Use encryption mechanisms such as AWS Key Management Service (KMS) for encrypting data at rest.

Implement SSL/TLS for encrypting data in transit.

Use secure protocols for communication between instances.

Apply strict IAM policies, NACLs, and Security Groups to control access.

Regularly audit and monitor access logs for security compliance.

. Question: What is the significance of a Transit Gateway in a VPC architecture, and when would you use it?

Answer: A Transit Gateway is used to simplify network connectivity in complex VPC architectures. It acts as a central hub for connecting multiple VPCs, VPNs, and Direct Connect connections. Instead of creating individual VPC peering connections between every VPC pair, you can use a Transit Gateway to create a more scalable and manageable network design. It is particularly useful in large-scale multi-VPC architectures where simplified routing and connectivity are essential.

9. Question: Explain the concept of VPC Endpoints and give an example of when you might use them.

Answer: VPC Endpoints allow private communication between your VPC and supported AWS services without using the public internet. For example, you can create an S3 VPC Endpoint to enable your EC2 instances to access Amazon S3 privately. This is useful when you want to enhance security, reduce data transfer costs, and improve performance by avoiding internet routing for specific AWS services.

10. Question: How do you design and implement a disaster recovery (DR) strategy for a VPC-hosted application?

Answer: A disaster recovery strategy for a VPC-hosted application typically involves:

Setting up a standby environment in a different AWS region.
Regularly replicating data and configurations to the secondary region using tools like AWS Backup or cross-region replication.
Implementing failover mechanisms, such as Route 53 DNS failover or an AWS Global Accelerator, to redirect traffic to the secondary region in case of a disaster.
Ensuring that both regions have the necessary compute and storage resources to handle the failover workload.
Testing the DR plan regularly to verify its effectiveness.

11. Question: What is AWS PrivateLink, and how does it enhance security in a VPC?

Answer: AWS PrivateLink is a service that enables private network connections between your VPC and supported AWS services or SaaS solutions over the AWS backbone network. It enhances security by keeping network traffic within the AWS network and avoids exposing traffic to the public internet. PrivateLink is beneficial for scenarios where data privacy, security, and compliance are top priorities.

12. Question: When would you use AWS Site-to-Site VPN vs. AWS Direct Connect for connecting an on-premises network to a VPC?

Answer: You would use AWS Site-to-Site VPN when you need a cost-effective and flexible solution for secure communication over the public internet. It is suitable for smaller data transfer needs and is easier to set up. AWS Direct Connect, on the other hand, provides dedicated, private, and high-bandwidth connections, making it ideal for large-scale, mission-critical workloads with strict latency and performance requirements.

13. Question: How can you implement fine-grained access control for resources within a VPC using IAM roles and policies?

Answer: To implement fine-grained access control:

Create IAM roles with specific permissions for EC2 instances or other AWS resources within your VPC.
Attach IAM policies to these roles, defining what actions and resources are allowed.
Associate the IAM roles with the resources that need the defined permissions.
Ensure that EC2 instances have the necessary IAM roles assigned.
Regularly review and audit IAM policies to maintain least privilege access.

14. Question: What is the purpose of VPC Flow Logs, and how can they be used for security and troubleshooting?

Answer: VPC Flow Logs capture information about network traffic within your VPC, allowing you to monitor and analyze network behavior. They can be used for:

Security: Detect and investigate suspicious traffic patterns.
Troubleshooting: Identify network issues, diagnose connectivity problems, and analyze traffic flow.
Compliance: Maintain records of network activity for auditing and compliance purposes.

Scenario 1: Network Isolation and Security

Question: You are designing a VPC for a company that needs to keep its application servers isolated from the public internet while allowing database servers to access the internet for software updates. How would you set up the VPC to meet these requirements?

Answer: To meet this requirement:

Create a VPC with both public and private subnets.
Place application servers in the private subnet.
Place database servers in the private subnet as well.
Create a NAT Gateway in the public subnet.
Configure the route table for the private subnet to route traffic to the NAT Gateway for internet access.
Use Security Groups to control inbound and outbound traffic for both application and database servers. Allow only necessary traffic.
This setup allows database servers to access the internet while keeping the application servers isolated from direct internet access.

Scenario 2: Multi-AZ Redundancy

Question: A critical web application needs to be highly available and fault-tolerant. How would you design a VPC to achieve this, ensuring that the application can continue to operate even if one Availability Zone (AZ) experiences a failure?

Answer: To ensure high availability and fault tolerance:

Create a VPC with multiple subnets, each in a different AZ.
Deploy application servers across these AZs.
Use an Elastic Load Balancer (ELB) to distribute traffic evenly across the instances in different AZs.
Set up database servers with Multi-AZ deployment for automatic failover.
Implement health checks and auto-scaling to replace unhealthy instances.
Configure Route 53 with latency-based routing or a failover routing policy for DNS-based failover.

This design ensures that the application can continue to operate even if one AZ experiences a failure, providing high availability.

Scenario 3: Hybrid Cloud Connectivity

Question: Your organization wants to extend its on-premises data center to AWS for scalability. How would you set up a VPC to securely connect the on-premises network with the AWS resources?

Answer: To securely connect the on-premises network to AWS:

Create a VPC with private and public subnets.
Set up a VPN connection or AWS Direct Connect to establish connectivity between the on-premises network and the VPC.
Configure appropriate route tables and security groups to control traffic flow.
Use a Virtual Private Gateway (VGW) or a Customer Gateway (CGW) for VPN connections.
For Direct Connect, provision a Direct Connect Gateway if connecting to multiple VPCs.
Ensure that your on-premises network has the necessary hardware or software VPN appliances or Direct Connect connections.

This setup allows for a secure and private connection between the on-premises data center and AWS resources, enabling hybrid cloud architecture.

Scenario 4: VPC Peering

Question: Your organization has multiple AWS accounts, each with its VPC. You want to enable private communication between resources in different VPCs. How would you set up VPC peering to achieve this?

Answer: To enable private communication between resources in different VPCs:

Establish VPC peering connections between the desired VPC pairs.
Configure the route tables in each VPC to include routes for the other VPC's CIDR block via the peering connection.
Ensure that the security groups and NACLs allow the necessary traffic between the peered VPCs.
Note that VPC peering is not transitive, so if you need communication between more than two VPCs, establish direct peering connections.
VPC peering allows private communication between resources in different VPCs, making it easier to share data and resources across AWS accounts.

Scenario 5: Network Isolation and Segmentation

Question: You are designing a VPC for a large e-commerce website. The website has a frontend, a backend, and a payment processing system. How would you set up the VPC to ensure network isolation and proper segmentation of these components for security reasons?

Answer: To ensure network isolation and segmentation:

Create a VPC with multiple private subnets and public subnets.
Place the frontend servers in the public subnets to interact with the internet.
Place the backend servers in private subnets, allowing them to communicate with the frontend servers but not directly with the internet.
Place the payment processing servers in a highly secured private subnet with restricted access only from the backend servers.
Use Security Groups and NACLs to control traffic between subnets, allowing only necessary communication.
Implement a Web Application Firewall (WAF) or security measures to protect the frontend servers from web-based attacks.

This setup ensures that the frontend, backend, and payment processing systems are properly segmented for security while maintaining network isolation.

Scenario 6: Disaster Recovery

Question: Your company operates a critical application in a VPC, and you want to ensure disaster recovery. How would you set up the VPC to have a reliable backup in another AWS region?

Answer: To set up disaster recovery across AWS regions:

Create a VPC in a secondary AWS region.
Use AWS services like AWS Backup or Amazon S3 cross-region replication to back up essential data and configurations.
Set up an AWS Global Accelerator or Amazon Route 53 with health checks to route traffic to the VPC in the secondary region if the primary region experiences an outage.
Ensure that you have copies of your application's Amazon Machine Images (AMIs) in the secondary region.
Periodically test your disaster recovery plan to ensure its effectiveness.

This configuration provides a reliable backup in another region and minimizes downtime in case of a disaster.

Scenario 7: Secure Remote Access

Question: Your team needs secure remote access to instances within your VPC for maintenance and troubleshooting. How would you provide secure remote access while maintaining security best practices?

Answer: To provide secure remote access:

Use a Bastion Host or Jump Box in a public subnet as an entry point for remote access.
Restrict SSH or RDP access to the Bastion Host using Security Groups and NACLs.
Use SSH keys or RDP certificates for authentication instead of passwords.
Implement Multi-Factor Authentication (MFA) for added security.
Allow access from specific IP addresses or ranges for added control.
Regularly monitor and audit remote access logs for security compliance.

This setup ensures that remote access to instances is secure while adhering to security best practices.

Scenario 8: Compliance and Logging

Question: Your organization has strict compliance requirements for logging network traffic within the VPC. How would you configure VPC Flow Logs to meet these compliance needs?

Answer: To configure VPC Flow Logs for compliance:

Enable VPC Flow Logs for the VPC or specific subnets.
Specify the desired destination for flow logs, such as Amazon S3 or CloudWatch Logs.
Define the log format and fields to include in the logs.
Ensure that the IAM roles or permissions are correctly set to allow flow log creation and access to the chosen destination.
Regularly review and analyze the flow logs for security and compliance purposes.

This setup ensures that network traffic within the VPC is logged and can be audited to meet compliance requirements.

VPC
A Virtual Private Cloud (VPC) is a fundamental networking construct in Amazon Web Services (AWS) that allows you to create a logically isolated section of the AWS cloud where you can launch AWS resources. It essentially provides you with your own private network within the AWS cloud. Let's explore VPCs in detail:
Network Isolation: VPCs allow you to create a private, isolated network environment in the AWS cloud. This isolation ensures that your resources are not directly accessible from the internet or from other VPCs by default.
Customizable IP Address Range: When you create a VPC, you specify an IP address range using Classless Inter-Domain Routing (CIDR) notation (e.g., 10.0.0.0/16). This IP address range defines the address space available for your VPC, and you can segment it into subnets based on your needs.
Subnets: Within a VPC, you can create one or more subnets. Subnets are logical divisions of the IP address range that you defined for the VPC. Subnets are associated with Availability Zones (AZs) in a region, allowing you to distribute your resources across multiple data centers for high availability.
Internet Connectivity: By default, resources in a VPC are not directly accessible from the internet. To make resources accessible from the internet, you can create a public subnet and attach an Internet Gateway (IGW) to it. Instances in the public subnet can have Elastic IP addresses or public IPv4 addresses, allowing them to communicate with the internet.
Private Subnets: Resources in private subnets do not have direct internet access. To provide internet access to instances in private subnets, you can use Network Address Translation (NAT) Gateways or NAT Instances located in the public subnet.
Security Groups: VPCs use Security Groups (SGs) as a virtual firewall for controlling inbound and outbound traffic at the instance level. You can specify rules in SGs to control traffic to and from instances.
Network ACLs: Network Access Control Lists (NACLs) are stateless firewalls that operate at the subnet level. NACLs allow you to control traffic by defining rules for each subnet, providing an additional layer of security.
VPC Peering: VPC Peering enables you to establish private network connections between different VPCs, even in different AWS accounts. It allows resources in different VPCs to communicate with each other as if they were on the same network.
VPN and Direct Connect: You can connect your on-premises data centers or remote networks to your VPC using Virtual Private Network (VPN) connections or AWS Direct Connect. This enables hybrid cloud architectures and secure communication between your on-premises infrastructure and AWS resources.
Transit Gateway: AWS Transit Gateway simplifies network connectivity between VPCs, data centers, and remote offices, making it easier to scale and manage large-scale network architectures.
VPC Endpoints: VPC Endpoints enable private connections between your VPC and AWS services, such as Amazon S3 and DynamoDB, without requiring internet traffic to traverse a public gateway.
In summary, AWS VPCs provide a flexible and secure way to create and manage your network infrastructure in the cloud. You can design and configure VPCs to meet your specific requirements, ensuring network isolation, security, and connectivity for your AWS resources. VPCs are a fundamental building block for constructing a wide range of AWS architectures, from simple web applications to complex enterprise solutions.
Why VPC is needed
A Virtual Private Cloud (VPC) is needed in cloud computing, especially within platforms like Amazon Web Services (AWS), for several key reasons:
Network Isolation: VPC provides a private, isolated network environment within a public cloud platform like AWS. This isolation ensures that your cloud resources are not exposed to the public internet by default. It allows you to build and manage your own network infrastructure securely.
Custom IP Address Range: When you create a VPC, you can define the IP address range (CIDR block) for your virtual network. This gives you full control over IP address assignment and subnetting, allowing you to design your network according to your specific requirements.
Resource Segmentation: VPC allows you to create multiple subnets within your virtual network. These subnets can be distributed across different Availability Zones (AZs) in a region. This segmentation helps with resource organization, improves fault tolerance, and allows you to implement different security policies for different parts of your application.
Security Control: VPC enables granular control over network security. You can use Network Access Control Lists (NACLs) and Security Groups (SGs) to define rules for inbound and outbound traffic, ensuring that your resources are only accessible by authorized entities. This control is crucial for maintaining a secure cloud environment.
Internet Connectivity: While VPCs provide isolation, you can configure them to allow specific resources, typically located in public subnets, to have controlled access to the public internet. This is essential for resources that need to communicate with external services or users.
Private Subnets: VPC allows you to create private subnets where resources are not directly exposed to the internet. To provide internet access for resources in private subnets, you can use Network Address Translation (NAT) gateways or instances in public subnets.
Hybrid Cloud Connectivity: VPC provides tools like VPN connections and AWS Direct Connect to securely connect your on-premises data centers or remote locations to your cloud resources. This facilitates hybrid cloud architectures and seamless communication between your on-premises and cloud environments.
VPC Peering: VPCs can be peered together to allow private communication between resources in different VPCs, even if they belong to different AWS accounts. This is useful for sharing resources or data securely across different projects or teams.
Scalability and Elasticity: VPCs are highly scalable. You can easily add or remove resources, adjust network configurations, and expand your network as your business or application requirements change. This flexibility is vital for handling dynamic workloads.
Network Monitoring and Logging: VPCs provide features like VPC Flow Logs, which allow you to capture and analyze network traffic, aiding in security monitoring, compliance, and troubleshooting.
Data Privacy and Compliance: VPCs are designed to help organizations meet data privacy and compliance requirements by providing the tools and controls needed to protect sensitive data and ensure compliance with regulations.
In summary, a VPC is essential for building and managing a secure, isolated, and customizable network environment within a cloud infrastructure. It gives you the control and flexibility needed to deploy and operate cloud resources while meeting security, compliance, and scalability requirements. VPCs are a fundamental building block for modern cloud-based applications and services.
Why VPC is required and what it contains
A Virtual Private Cloud (VPC) is required for several reasons in cloud computing, and it typically contains the following elements:

Why VPC is Required:
Isolation: A VPC provides network isolation within a cloud environment. It allows you to create your private network, separate from other users in the cloud, ensuring that your resources are not accessible by default to the public internet or other VPCs.
Security: VPCs offer robust security controls, such as Network Access Control Lists (NACLs) and Security Groups (SGs), that help you define and enforce network traffic rules. This isolation and security are crucial for protecting your data and applications from unauthorized access.
Customization: VPCs allow you to customize your network, including IP address ranges, subnets, routing tables, and security policies. This customization enables you to design your network infrastructure according to your specific requirements.
Scalability: VPCs are scalable, allowing you to expand your network as your business grows. You can add or remove resources, adjust configurations, and adapt to changing workloads easily.
Connectivity: VPCs offer various connectivity options, such as Virtual Private Network (VPN), AWS Direct Connect, VPC peering, and Transit Gateways, which enable you to connect your cloud resources to on-premises data centers, other VPCs, or external networks securely.
Resource Management: VPCs provide a structured way to organize and manage your cloud resources. You can create subnets, assign resources to specific subnets, and control access between them. This organization simplifies resource management and maintenance.
What a VPC Contains:

A typical VPC contains the following components:

IP Address Range: When you create a VPC, you define an IP address range using CIDR notation (e.g., 10.0.0.0/16). This address range defines the available private IP addresses for your VPC.
Subnets: Within a VPC, you create subnets, which are like smaller sections of your VPC. Subnets are typically associated with specific Availability Zones (AZs) within a region.
Route Tables: VPCs have route tables that determine how network traffic is directed within the VPC. You can configure route tables to route traffic between subnets and control where traffic goes.
Security Groups: Security Groups are used to control inbound and outbound traffic to instances within a VPC. They act as virtual firewalls at the instance level.
Network Access Control Lists (NACLs): NACLs are stateless firewalls that operate at the subnet level. They help control traffic in and out of subnets based on defined rules.
Internet Gateway (IGW): An IGW allows resources in public subnets to connect to the internet while keeping resources in private subnets isolated. It serves as the gateway for outbound and inbound internet traffic.
NAT Gateways/Instances: Network Address Translation (NAT) Gateways or Instances are used to enable private instances in a VPC to access the internet for software updates or other purposes, while still maintaining security.
Peering Connections: VPCs can be peered together to allow private communication between them, making it easier to connect resources in different VPCs.
VPN or Direct Connect: VPCs can be connected to on-premises networks using VPN or AWS Direct Connect for secure communication between cloud and on-premises resources.
Transit Gateway: For more complex architectures, Transit Gateway can be used to simplify network connectivity and routing between multiple VPCs and on-premises networks.
In summary, a VPC is required to create a secure, customizable, and isolated network environment in a cloud platform like AWS. It contains various components and configurations that help you design and manage your network infrastructure effectively.

Windows Debugging tools

2023-08-08T07:22:00.000-07:00

Process Monitor (ProcMon): This tool monitors file system, registry, and process/thread activity in real-time. It helps identify issues with file access, registry changes, and process interactions.

Process Explorer: Process Explorer is a powerful task manager replacement that provides detailed information about running processes, including their associated DLLs and network connections.

WinDbg: WinDbg is a powerful debugger provided by Microsoft that allows you to inspect and debug user-mode and kernel-mode processes. It's useful for analyzing crash dumps and diagnosing complex issues.

WinObj: WinObj provides a graphical view of the Windows object namespace, allowing testers to explore objects like files, directories, devices, and more.

Dependency Walker: Dependency Walker helps in analyzing dependencies and potential issues with DLLs and EXEs, making it useful for identifying missing or incompatible dependencies.

AppVerifier: AppVerifier is a testing tool designed to help identify and diagnose issues in applications, including security-related problems and compatibility issues.

Sysinternals Suite: This is a collection of various powerful Windows utilities developed by Mark Russinovich and acquired by Microsoft. It includes tools like Process Monitor (ProcMon), Process Explorer, Autoruns, and many others.

Windows Performance Toolkit (WPT): This toolkit provides tools like Xperf and WPR (Windows Performance Recorder) to profile and diagnose system performance issues.

Wireshark: Though not exclusively a Windows internals tool, Wireshark is essential for analyzing network traffic and identifying potential malware communication.

Process Hacker: Process Hacker is an open-source tool similar to Process Explorer, offering advanced monitoring and manipulation of system processes and services.

Remember that software tools and technologies are continuously evolving, so it's crucial to stay up-to-date with the latest tools and techniques used in the industry. Always ensure that you are using these tools responsibly and in accordance with your organization's policies.

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What is a memory dump?

A memory dump is the process of taking all information content in RAM and writing it to a storage drive as a memory dump file (*.DMP format).

1) What is a memory dump, and why is it useful in Windows troubleshooting?

A memory dump, also known as a crash dump or a system dump, is a snapshot of the contents of a computer's random-access memory (RAM) at a specific moment when a system crash or a "blue screen of death" (BSOD) occurs in Windows operating systems. When a critical system error occurs, Windows may create a memory dump file to capture the state of the system at the time of the crash.

Memory dumps are useful in Windows troubleshooting for several reasons:

Debugging System Crashes: When a system encounters a critical error and crashes, the exact cause of the crash may not be immediately apparent. Analyzing the memory dump can provide valuable information about the state of the system, the processes running, and the drivers in use at the time of the crash. This data can help identify the root cause of the issue and facilitate troubleshooting.

Understanding Blue Screen Errors: Blue Screen of Death (BSOD) errors are often accompanied by cryptic error codes that are difficult for users to interpret. Memory dumps contain more detailed information about the system's state at the time of the crash, including the error code and relevant debugging data. This can assist in deciphering the cause of the BSOD.

Reconstructing Events: Memory dumps are like snapshots of the system's memory, allowing analysts or support personnel to review the state of the system just before the crash. This can help reconstruct the events leading up to the crash, such as the sequence of processes and the behavior of drivers.

Debugging Application Issues: Memory dumps can also be created for individual applications when they encounter errors or crashes. These dumps, known as application crash dumps, provide developers with valuable information to diagnose and fix application-specific issues.

Remote Troubleshooting: In some cases, memory dumps can be collected and analyzed remotely, allowing support personnel to investigate and troubleshoot system crashes without direct access to the affected machine.

There are different types of memory dumps that can be created in Windows, including:

Small Memory Dump (Minidump): Contains basic information about the crash, such as the stop code and the memory addresses of the crash location. It is smaller in size and is often used for most troubleshooting scenarios.
Kernel Memory Dump: Contains information about the kernel memory at the time of the crash. It provides more comprehensive data than a minidump but is still smaller in size than a full memory dump.
Complete Memory Dump: Captures the entire contents of the system's RAM at the time of the crash. It is the largest memory dump type and provides the most detailed information for debugging, but it requires significant disk space.

Memory dumps can be essential tools for system administrators, developers, and support personnel to diagnose and resolve complex issues that result in system crashes or application errors in Windows environments.

2) Explain the differences between a complete memory dump, kernel memory dump, and small memory dump.

The main differences between a complete memory dump, kernel memory dump, and small memory dump lie in the amount of information they capture and the size of the resulting dump file. Each type of memory dump serves different purposes and has specific use cases. Let's explore the differences:

1. Complete Memory Dump:

Description: As the name suggests, a complete memory dump captures the entire contents of the computer's RAM at the time of a system crash. It includes the data in use by the operating system, applications, and drivers, providing a comprehensive snapshot of the system's memory.
File Size: Complete memory dumps are the largest among the three types, potentially taking up a considerable amount of disk space, often several gigabytes in size.
Use Cases: Complete memory dumps are primarily used when detailed debugging information is required to investigate complex system crashes. They provide the most comprehensive data, allowing in-depth analysis of the crash for advanced debugging scenarios.

2. Kernel Memory Dump:
Description: A kernel memory dump captures only the kernel memory space, which contains essential data about the Windows kernel and device drivers. It omits the data of user-mode applications, resulting in a smaller dump file compared to a complete memory dump.
File Size: Kernel memory dumps are larger than small memory dumps but smaller than complete memory dumps. Their size can vary but is typically several hundred megabytes.
Use Cases: Kernel memory dumps are often used for troubleshooting crashes related to drivers or kernel-level issues. They provide enough information to analyze most system crashes without co0nsuming excessive disk space.

3. Small Memory Dump (Minidump):
Description: A small memory dump captures a minimal amount of information about the crash. It includes the stop code, some key data structures, and the contents of the stack trace for each thread at the time of the crash. However, it does not include much user-mode or kernel-mode memory data.
File Size: Small memory dumps are significantly smaller than both complete and kernel memory dumps. They are usually a few megabytes in size.
Use Cases: Small memory dumps are widely used for routine troubleshooting of system crashes. They provide enough data to identify the cause of many common BSOD errors and are the default dump type in most Windows systems.

How do you generate a memory dump on a Windows system manually?

To manually generate a memory dump on a Windows system, you can use the built-in utility called "Windows Error Reporting" (WER) or configure the system to create memory dumps when specific types of crashes occur. Here's how you can do it:

Method 1: Generating a Manual Memory Dump via Windows Error Reporting (WER):

Trigger the System Crash:

To generate a memory dump manually, you need to trigger a system crash (a "blue screen" crash). You can do this by pressing the keyboard combination "Right Ctrl" + "Scroll Lock" (twice) + "Scroll Lock." This key combination is designed to cause a system crash and initiate the memory dump process.

2. Check for Memory Dump File:

After the crash, the memory dump file will be created in the default dump file location, typically in the %SystemRoot%\Minidump folder. The file will have a ".dmp" extension and contain information about the crash.

Method 2: Configuring Automatic Memory Dumps:

You can also configure Windows to automatically generate memory dumps when specific types of crashes occur. To do this, follow these steps:

1. Open System Properties:

Right-click on "This PC" or "My Computer" and select "Properties." Alternatively, you can press the "Windows key + Pause/Break" to open the System window.

2. Access Advanced System Settings:

In the System window, click on "Advanced system settings" on the left-hand side. This will open the System Properties dialog box.

3. Open Startup and Recovery Settings:

In the System Properties dialog box, click on the "Settings" button under the "Startup and Recovery" section.

4. Configure Dump Settings:

In the Startup and Recovery dialog box, under the "System failure" section, you can configure the type of memory dump to be generated when the system encounters a crash. You have three options:

Small memory dump (Minidump): This is the default option and usually sufficient for most troubleshooting scenarios.
Kernel memory dump: Provides more information than a minidump but is smaller than a complete memory dump.
Complete memory dump: Captures the entire contents of the system's RAM but requires significant disk space.

Select the desired type of dump from the dropdown list.

5. Save Changes:

Click "OK" to apply the changes and close the Startup and Recovery dialog box.

After configuring these settings, Windows will automatically generate memory dumps according to your selection when a system crash occurs.

Please note that generating a memory dump manually via WER is useful for testing purposes or if you need to capture a dump immediately when a system is experiencing issues. The automatic memory dump configuration is more suitable for routine troubleshooting and capturing dumps when you cannot manually initiate a crash.

Which tool(s) do you use to analyze memory dumps, and why?

The choice of tool depends on the type of analysis required and the expertise of the user. Here are a few commonly used tools:

1. WinDbg (Windows Debugger):
WinDbg is a powerful and advanced debugger provided by Microsoft as part of the Windows SDK (Software Development Kit). It is a command-line tool designed for kernel-mode and user-mode debugging. It is commonly used for deep analysis of memory dumps and diagnosing complex system crashes. WinDbg supports various commands for inspecting memory, examining data structures, and analyzing call stacks.

2. Visual Studio Debugger:
For developers using Microsoft Visual Studio, the built-in debugger can also be used to analyze memory dumps. Visual Studio supports post-mortem debugging, which allows you to load a memory dump and inspect the state of the application at the time of the crash. This is especially useful for diagnosing application-specific issues.

3. DebugDiag (Debug Diagnostic Tool):
DebugDiag is a user-friendly graphical tool provided by Microsoft to help diagnose memory-related issues in Windows applications. It can analyze memory dumps and provide reports with detailed information about potential memory leaks, crashes, and performance problems.

4. ProcDump:
ProcDump is a command-line utility provided by Microsoft's Sysinternals suite. It can generate memory dumps based on specific criteria, such as CPU usage, memory usage, or unhandled exceptions. It is useful for capturing dumps of specific processes when certain conditions are met.

5. BlueScreenView:
BlueScreenView is a lightweight and user-friendly tool that does not perform in-depth debugging but can quickly analyze minidump files created during BSOD crashes. It provides a simplified view of the crash details, including the stop code and related information.

6. WinCrashReport:
WinCrashReport is another user-friendly tool that reads and displays crash reports from memory dump files. It provides an easy-to-read summary of the crash data and can be useful for quick analysis.
It's important to note that analyzing memory dumps can be a complex task, especially for kernel-mode debugging. Knowledge of debugging techniques, system internals, and programming is often required to interpret the information correctly and identify the root cause of the crash. Therefore, users should choose a tool that matches their level of expertise and the type of analysis they need to perform.

Can you mention some of the common causes of system crashes that might be identified from memory dump analysis?

Memory dump analysis can reveal valuable insights into the causes of system crashes on Windows systems. While the specific cause may vary depending on the crash and the system's configuration, here are some common issues that memory dump analysis might identify:

1. Faulty or Incompatible Device Drivers:
Outdated, improperly installed, or incompatible device drivers can cause system crashes. Memory dump analysis may point to specific drivers as the root cause of the crash.

2. Hardware Issues:
Problems with hardware components like faulty RAM, overheating, or failing hard drives can lead to system crashes. Memory dump analysis may provide clues about hardware-related errors.

3. Software Conflicts:
Conflicts between different software components, such as third-party applications, drivers, or system services, can cause crashes. Memory dump analysis may highlight conflicts between modules.

4. Memory Corruption:
Memory corruption can occur due to various reasons, including software bugs, faulty hardware, or malicious software. Memory dump analysis may reveal signs of memory corruption.

5. Stack Overflow or Stack Underflow:
Stack overflow occurs when a program exhausts its available stack space, while stack underflow happens when it accesses an invalid memory location in the stack. Memory dump analysis can identify these issues.

6. Heap Corruption:
Heap corruption occurs when a program accesses memory beyond the bounds of allocated heap blocks, leading to undefined behavior and crashes. Memory dump analysis may detect signs of heap corruption.

7.Invalid or NULL Pointer Dereferences:
Dereferencing an invalid or NULL pointer can lead to access violation errors and cause system crashes. Memory dump analysis can pinpoint the locations where these errors occurred.

8. Resource Exhaustion:
Running out of system resources like memory, handles, or disk space can trigger crashes. Memory dump analysis may indicate resource exhaustion issues.

9. Interrupt Conflicts:
Interrupt conflicts between hardware devices or drivers can cause system instability. Memory dump analysis may uncover conflicts related to hardware interrupts.

10. Malware or Viruses:
Malicious software can cause crashes by corrupting critical system files or causing unexpected behavior. Memory dump analysis may reveal signs of malware activity.

Remember that memory dump analysis can be complex and requires expertise in debugging techniques and system internals. Identifying the exact cause of a system crash may involve a thorough investigation and may not always be immediately apparent from the memory dump alone. In some cases, multiple factors may contribute to a crash, making it essential to carefully analyze the data and gather additional information if needed.

Walk us through the steps you would take to analyze a memory dump and identify the cause of a system crash.

step-by-step guide for analyzing a memory dump to identify the cause of a system crash on a Windows system. Please note that memory dump analysis can be complex, and the steps may vary depending on the specific crash scenario and the tools being used. Here's a high-level overview of the process:

Step 1: Collect the Memory Dump
Obtain the memory dump file generated during the system crash. Depending on the configuration, this could be a small memory dump (minidump), a kernel memory dump, or a complete memory dump.

Step 2: Install Debugging Tools
If you haven't already, download and install the appropriate debugging tools for Windows. The most commonly used tool for memory dump analysis is WinDbg.

Step 3: Open the Memory Dump in WinDbg
Launch WinDbg, either the standalone version or the one provided with Visual Studio, and load the memory dump file using the "File" menu.

Step 4: Set Symbol File Path
To analyze the memory dump effectively, WinDbg requires access to the correct symbol files that correspond to the version of Windows and its components installed on the crashed system. Set the symbol file path in WinDbg using the "File" menu > "Symbol File Path."

Step 5: Analyze the Crash Dump
Examine the crash details, including the stop code and bug check parameters. These details can provide valuable information about the nature of the crash.

Step 6: Review the Call Stack
Examine the call stack to see the sequence of function calls leading up to the crash. The call stack can help identify the point of failure and the involved modules.

Step 7: Identify the Faulting Module
Determine the module or driver responsible for the crash by analyzing the call stack and memory contents. This module is often indicated by a filename in the call stack.

Step 8: Check for Known Issues or Bug Reports
Research the identified module or driver to check if there are any known issues, bug reports, or updates related to it. Sometimes, the vendor may have released a fix or update that addresses the problem.

Step 9: Update Drivers and Software
If the crash is caused by outdated or incompatible drivers or software, update them to the latest versions to see if it resolves the issue.

Step 10: Analyze Memory and Data Structures
Use WinDbg commands and extensions to inspect memory, data structures, and registers to identify potential memory corruption, pointer issues, or other anomalies.

Step 11: Conduct Further Analysis (Optional)
For more complex issues, you may need to analyze specific sections of memory, examine thread states, or perform kernel-mode debugging. This may require deeper knowledge and expertise in debugging techniques.

Step 12: Test and Verify
If you find a potential solution or fix, test it to verify whether it resolves the issue and prevents future crashes.

Remember that memory dump analysis requires a good understanding of debugging concepts, operating system internals, and programming. Additionally, some crashes may be caused by a combination of factors, making the analysis process more intricate. Professional developers, system administrators, or support personnel often carry out in-depth memory dump analysis to diagnose and resolve complex system crash issues.

How do you determine if a memory dump indicates a hardware issue or a software/driver problem?

Determining whether a memory dump indicates a hardware issue or a software/driver problem requires careful analysis of the crash details and the context surrounding the crash. Here are some key steps and indicators to help differentiate between the two:

1.Analyze the Stop Code and Bug Check Parameters:
The stop code and bug check parameters displayed in the memory dump provide valuable information about the nature of the crash. Some bug check codes are specifically associated with hardware issues (e.g., "0x124" for hardware-related WHEA_UNCORRECTABLE_ERROR), while others are more likely related to software issues (e.g., "0x3B" for SYSTEM_SERVICE_EXCEPTION).

2. Check for Known Driver or Software Issues:
If the crash is related to a specific driver or software module, check for known issues or bug reports associated with that component. Driver-related crashes are common, and vendors may release updates or hotfixes to address such issues.

3.Review the Call Stack:
Examine the call stack to see the sequence of function calls leading up to the crash. Hardware-related crashes might have less informative call stacks, while software or driver-related crashes may show a more detailed sequence of calls involving specific modules.

4. Inspect the Memory Contents:
Analyze the memory contents and data structures to identify potential memory corruption or invalid pointer references. Memory corruption issues are more likely to be software-related, although certain hardware faults can also lead to memory corruption.

5. Consider the Context of the Crash:
Take into account the context in which the crash occurred. If the crash is triggered consistently during specific tasks or actions, it may suggest a software or driver problem. On the other hand, random and unpredictable crashes may be indicative of a hardware issue.

6. Check Event Logs and System Information:
Examine the system's event logs and system information for any other relevant error messages or indications of hardware problems, such as disk errors, temperature warnings, or memory-related events.

7.Review Minidump vs. Full Memory Dump:
If you have a full memory dump, it may provide more comprehensive information about the system state at the time of the crash, making it easier to identify hardware-related issues. Minidumps may have limited data, making it more challenging to determine the root cause.

8.Perform Hardware Diagnostics:
If you suspect a hardware issue based on the memory dump analysis, consider running hardware diagnostics on the system, including memory tests, hard drive tests, and temperature monitoring.

It's important to note that the distinction between hardware and software/driver problems may not always be clear-cut, as some issues can have mixed causes or interactions between hardware and software. In complex cases, a thorough analysis may involve a combination of memory dump analysis, event log examination, hardware diagnostics, and further testing.

For critical systems or situations where you're uncertain about the cause of the crash, it's advisable to seek the expertise of experienced system administrators, developers, or support personnel to perform a detailed investigation.

What are the most common debugging commands you use while analyzing a memory dump?

list of common debugging commands used by analysts and developers when analyzing a memory dump with WinDbg. These commands help inspect memory, examine data structures, analyze call stacks, and extract relevant information from the dump file. Here are some of the most commonly used commands:

1. !analyze -v:
This is one of the most frequently used commands to trigger automatic analysis of the crash dump and obtain a preliminary summary of the crash information, including the stop code, bug check parameters, and a probable cause.

2. kv or k:
These commands display the current thread's call stack. "kv" provides a verbose output with source file and line number information, while "k" displays a shorter version without additional details.

3. lm (list modules):
This command lists all the loaded modules (drivers and libraries) with their base addresses, sizes, and symbols.

4. !process 0 0:
This command lists all the running processes along with their process IDs (PIDs) and parent process IDs (PPIDs).

5. !thread:
This command displays information about the current threads in the system, including their IDs, states, and stack traces.

6. !poolused or !poolused X:
These commands display information about the pool memory usage, showing the number of bytes used in each pool tag. "X" can be replaced with a pool tag to see memory usage for a specific pool type.

7. !mex.m:
This command displays the contents of the MmSubsectionBase field of the system's memory manager. It can be useful for investigating memory sections.

8. dt (display type):
This command allows you to display the contents of a data structure defined by a specific type. For example, "dt nt!_ETHREAD" displays the contents of the ETHREAD (executive thread) structure.

9. !address:
This command displays information about a specific memory address, such as the allocation size, protection, and region details.

10. !error (error code):
This command provides a description of a given error code. It's helpful for understanding the meaning of specific error codes seen in the crash analysis.

11. !handle X:
This command displays information about handles in the system, where "X" is the process ID (PID) of the target process.

These commands represent only a fraction of the many available commands in WinDbg and other debugging tools. The appropriate commands to use depend on the nature of the crash and the specific details you want to investigate during the memory dump analysis. Debugging experts often develop a proficiency in using these commands and understanding how to interpret the output to diagnose and resolve system crashes effectively.

Explain the concept of "bug check codes" (stop codes) and their significance in memory dump analysis.

In the context of Windows operating systems, a "bug check code," also known as a "stop code," is a unique hexadecimal number that is associated with a specific type of system crash or "blue screen of death" (BSOD). When a critical error occurs in Windows, the system generates a memory dump to capture the state of the system at the time of the crash. The memory dump contains valuable information that helps in diagnosing the cause of the crash, and the bug check code is a crucial piece of this information.

The bug check code is usually displayed on the BSOD screen and is also included in the memory dump file. It indicates the nature of the error that caused the crash and provides a starting point for memory dump analysis. Each bug check code is associated with a specific "Bug Check Code Reference" in Microsoft's documentation, which explains the meaning and potential causes of the error.

The significance of bug check codes in memory dump analysis includes:

1. Identifying the Nature of the Crash: The bug check code helps identify the specific type of system crash that occurred. Different bug check codes correspond to various types of errors, such as memory corruption, driver issues, hardware faults, system service exceptions, etc.

2. Narrowing Down the Cause: Memory dump analysis can be complex, but the bug check code narrows down the scope of investigation. It helps focus the analysis on the likely causes associated with that particular error code.

3. Troubleshooting and Debugging: With the bug check code, developers, system administrators, and support personnel can search for relevant documentation and online resources to understand the potential causes and solutions for the specific error.

4. Filtering and Organizing Memory Dumps: In large environments with many systems generating memory dumps, bug check codes can be used to categorize and organize the crash data for easier management and analysis.

For example, some common bug check codes include:

0x0000001A: MEMORY_MANAGEMENT - Indicates memory-related issues like corruption or allocation errors.
0x000000D1: DRIVER_IRQL_NOT_LESS_OR_EQUAL - Typically caused by faulty drivers or hardware.
0x0000007E: SYSTEM_THREAD_EXCEPTION_NOT_HANDLED - Often associated with driver or software issues.
0x00000050: PAGE_FAULT_IN_NONPAGED_AREA - Indicates memory access errors.

When analyzing a memory dump, the first step often involves examining the bug check code to understand the general type of crash. From there, further analysis, such as examining the call stack, inspecting memory contents, and reviewing specific driver or module information, can be performed to pinpoint the root cause of the crash.

Overall, bug check codes play a vital role in memory dump analysis by providing essential clues about the nature of the crash and guiding the investigation process towards identifying and resolving the underlying issues.

Have you encountered any specific challenges while analyzing memory dumps? How did you overcome them?

1) Complexity and Expertise: Memory dump analysis requires a deep understanding of debugging techniques, operating system internals, and programming concepts. Overcoming this challenge involves building expertise through education, practice, and hands-on experience with debugging tools.

2. Data Overload: Memory dumps can contain a vast amount of data, making it challenging to identify relevant information. Analysts overcome this challenge by focusing on specific areas of interest, using commands to extract the needed data, and systematically narrowing down the scope of analysis.

Ambiguous Causes: Memory dumps may not always have clear and straightforward causes. An issue might have multiple contributing factors or involve interactions between software and hardware. Analysts address this by considering various possibilities, looking for patterns, and applying systematic analysis techniques.

False Positives: Automated analysis tools might provide preliminary findings that turn out to be false positives or not directly related to the actual issue. Overcoming this challenge requires manual verification and cross-referencing with other sources of information.

Unique Scenarios: Every crash can be unique, and the same bug check code might have different underlying causes in different contexts. Analysts must adapt their approach to accommodate the specific circumstances of each memory dump.

Resource Limitations: In some cases, resource limitations might prevent exhaustive analysis. This challenge can be managed by focusing on the most critical and likely causes first and gradually expanding the investigation if necessary.

Lack of Context: Memory dumps lack the real-time context of the system's behavior leading up to the crash. Analysts address this by combining memory dump analysis with event logs, system monitoring data, and user input to build a more complete picture.

Kernel-Mode Debugging: Debugging kernel-mode issues can be more complex than user-mode debugging due to lower-level system interactions. Overcoming this challenge requires familiarity with kernel debugging techniques and tools.

Intermittent Issues: Some issues may only occur intermittently, making them challenging to reproduce and analyze. To overcome this challenge, analysts may need to rely on detailed event logs, performance monitoring, and historical data.

Limited Information: Minidump files, while smaller and faster to generate, might lack the level of detail needed for in-depth analysis. Overcoming this challenge involves optimizing the use of available data and employing advanced techniques if required.

Overall, effective memory dump analysis involves a combination of expertise, systematic approaches, collaboration with peers, utilization of debugging tools, and a willingness to learn from each analysis to improve skills over time.

How would you analyze a memory leak using memory dump analysis?

Analyzing a memory leak using memory dump analysis involves identifying the processes or components responsible for excessive memory consumption and pinpointing the root cause of the leak. Here's a step-by-step guide on how to approach memory leak analysis using memory dump analysis techniques:

1. Collect the Memory Dump:
Capture a memory dump of the process or application that is exhibiting memory leak behavior. This can be done using tools like DebugDiag, ProcDump, or manual triggering if applicable.

2. Identify the Affected Process:
Determine the process or application that is consuming excessive memory. This could be evident from system monitoring, performance data, or user reports.

3. Open the Memory Dump:
Load the memory dump into a debugging tool like WinDbg or Visual Studio.

4. Analyze Heap Usage:
Use commands like !heap -s to analyze the heap usage within the process. Look for abnormal increases in heap allocations and deallocations over time.

5. Identify Leaked Objects:
Use the !heap -flt s command to filter heap allocations by specific criteria, such as allocation size or allocation call stack. This can help you identify leaked objects or allocations.

6.Inspect Call Stacks:
Examine the call stacks associated with leaked memory allocations to identify the code paths responsible for allocating memory that is not being deallocated.

7. Identify Responsible Code Paths:
Review the call stacks to identify the sections of code responsible for the memory allocations. This could involve application-specific code or third-party libraries.

8. Examine Object References:
Analyze the references to the leaked objects to understand why they are not being released. Look for references that prevent objects from being garbage-collected or deallocated.

9. Check for Circular References:
Circular references between objects can prevent proper garbage collection. Analyze references between objects to determine if circular references are contributing to the memory leak.

10. Examine Global Objects and Singletons:
Global objects or singleton patterns can sometimes lead to memory leaks if they are not properly managed. Investigate whether any such objects are contributing to the issue.

11. Inspect Finalization and Disposal:
If the language or framework supports finalization or disposal methods (e.g., C# IDisposable), ensure that objects are being properly finalized or disposed to release resources.

12. Review External Resources:
Memory leaks might also be related to external resources like file handles or network connections not being closed properly. Check for any resources that should be released but are not.

13.Test and Verify Fixes:
After identifying potential causes of the memory leak, implement fixes or optimizations to address the issues. Test the application thoroughly to ensure that the memory leak is resolved.

14.Monitor for Recurrence:
Continue monitoring the application over time to verify that the memory leak has been successfully addressed and does not reoccur.

Remember that memory leak analysis requires a solid understanding of programming languages, debugging tools, and memory management concepts. It's also essential to have a good grasp of the application's architecture and behavior to accurately identify the causes of the memory leak. Collaboration with developers and relevant stakeholders can provide valuable insights and help expedite the analysis and resolution process.

What is the difference between user-mode and kernel-mode memory dumps?

User-mode and kernel-mode memory dumps are two different types of memory dumps that capture different sets of data when a system crash occurs in a Windows operating system. These dumps are created to help diagnose issues and troubleshoot crashes, but they focus on different levels of the operating system and software components. Here's the difference between the two:

User-Mode Memory Dump:

Description: A user-mode memory dump captures the memory space of the user-mode processes that were running at the time of the crash. This includes the memory allocated for user applications and their associated modules.
Scope: User-mode dumps primarily focus on the memory and threads of user-level processes and do not include detailed information about kernel-mode components.
Usage: User-mode dumps are often used when diagnosing application crashes or issues that occur within user-level code. They are smaller in size compared to kernel-mode dumps, making them more manageable for analysis.

Kernel-Mode Memory Dump:

Description: A kernel-mode memory dump captures a broader set of data, including both user-mode and kernel-mode components. It captures the memory used by the Windows kernel, device drivers, and other operating system structures.
Scope: Kernel-mode dumps provide a more comprehensive view of the system's state at the time of the crash. They include information about processes, threads, system data structures, and device drivers.
Usage: Kernel-mode dumps are valuable for diagnosing system crashes, BSOD errors, and issues that involve interactions between user-mode applications and kernel-mode components. They are larger in size compared to user-mode dumps due to the additional data they capture.

When choosing between user-mode and kernel-mode memory dumps, consider the nature of the issue you're troubleshooting. If the problem is isolated to a specific application or user-mode component, a user-mode memory dump might provide sufficient information. On the other hand, if the issue involves system-level components, drivers, or kernel-mode interactions, a kernel-mode memory dump is more appropriate.

It's also worth noting that there are variations of these memory dumps, such as small memory dumps (minidumps) and complete memory dumps, which capture different amounts of data and can be chosen based on the complexity of the issue and available resources for analysis.

What is the default location of kernel memory dump?

On Windows systems, the default location for storing kernel memory dumps (also known as full memory dumps) can vary depending on the version of Windows and the configuration. By default, kernel memory dumps are usually stored in the system's root directory on the system drive (typically the C: drive), in a file named "MEMORY.DMP."

The full path to the default location of the kernel memory dump is often as follows:

C:\MEMORY.DMP

Please note that the actual location may vary, and in some cases, the memory dumps might be stored in a different directory or on a different drive, especially if the system drive has limited space.

If you're looking to locate or change the location of kernel memory dumps, you can do so through the following steps:

1. Locating the Default Kernel Dump Location:

Open File Explorer.
Navigate to the root directory of the system drive (usually the C: drive).
Look for the "MEMORY.DMP" file.

2. Changing the Dump File Location:

Open the "System Properties" dialog by right-clicking "This PC" or "My Computer" and selecting "Properties."
Click on "Advanced system settings" on the left-hand side.
In the "System Properties" dialog box, under the "Startup and Recovery" section, click the "Settings" button.
Under "Write debugging information," you can choose a different location for the dump file or configure a specific location for debugging symbols.

Keep in mind that modifying these settings might require administrative privileges. Additionally, it's essential to ensure that the selected location has sufficient

What are various reasons of kernel memory dump on windows

A kernel memory dump, also known as a full memory dump, is generated on Windows systems when a system crash or "blue screen of death" (BSOD) occurs. Kernel memory dumps capture a snapshot of the entire contents of the system's RAM at the time of the crash. Various issues can trigger a kernel memory dump, and these crashes can result from a range of factors. Here are some common reasons for kernel memory dumps on Windows:

Hardware Failures:
Hardware issues such as faulty RAM modules, overheating of components, failing hard drives, or defective hardware can cause system crashes that lead to kernel memory dumps.

Driver Issues:
Incompatible or outdated device drivers can cause instability in the system, leading to crashes. Kernel memory dumps might occur if a driver attempts to access invalid memory addresses or causes other critical errors.

Software Conflicts:
Conflicts between software components, including third-party applications and system services, can result in system crashes. Kernel memory dumps may occur when these conflicts lead to unhandled exceptions or critical errors.

System Service Failures:
Malfunctioning or crashing system services, which play a critical role in the operating system's functionality, can lead to crashes that trigger kernel memory dumps.

Kernel-Level Errors:
Errors occurring at the kernel level, such as invalid memory access, page faults, and other kernel-mode exceptions, can trigger kernel memory dumps. These errors are often indicative of deeper system issues.

Driver Verifier Detection:
Windows' Driver Verifier tool is used to identify driver-related issues. When enabled, Driver Verifier might detect violations in driver behavior and trigger crashes that result in kernel memory dumps.

Hardware Interrupt Conflicts:
Conflicts between hardware components or device drivers that handle hardware interrupts can cause system crashes. These crashes can result in kernel memory dumps.

Malware or Security Exploits:
Malicious software, viruses, or security exploits that compromise system integrity can lead to crashes that trigger kernel memory dumps.

Memory Corruption:
Memory corruption issues, whether caused by software bugs or hardware faults, can lead to system instability and crashes that result in kernel memory dumps.

Resource Exhaustion:
Running out of critical system resources, such as memory or kernel-mode resources, can lead to crashes that trigger kernel memory dumps.

Kernel memory dumps are crucial for diagnosing and resolving these issues because they provide a detailed snapshot of the system's state at the time of the crash. By analyzing the kernel memory dump, technicians and developers can gain insights into the root causes of the crashes and take appropriate steps to address them.

Can you explain the concept of virtual memory and its role in memory dump analysis?

Virtual memory is a memory management technique used by operating systems to provide an abstraction of the physical memory (RAM) and extend the available memory beyond the physical limitations of the hardware. It enables programs to address more memory than is physically installed in the system and allows the operating system to efficiently manage memory resources. Virtual memory plays a significant role in memory dump analysis, especially when analyzing system crashes and memory-related issues.

Here's how virtual memory works and its role in memory dump analysis:

How Virtual Memory Works:

1. Address Space: Each process running on a system has its own virtual address space, which is divided into pages. These virtual pages are the units of memory allocation and are typically smaller than physical memory pages.

2. Page Tables: The operating system maintains a data structure called a page table that maps virtual addresses to physical addresses. This mapping allows the system to access data stored in physical memory even if it's not directly accessible by the process.

3. Page Faults: When a process tries to access a virtual page that is not currently in physical memory (a situation called a page fault), the operating system triggers a page fault handler. The handler retrieves the required page from disk (if it's stored there) and updates the page table accordingly.

Role in Memory Dump Analysis:

Capturing the System State: When a system crash or BSOD occurs, a memory dump captures the state of the system's virtual memory, including both physical memory and data that has been paged out to disk. This allows analysis of the entire system's memory, not just the portion that fits into physical RAM.

Diagnosing Memory-Related Issues: Virtual memory plays a crucial role in diagnosing memory-related issues, such as memory leaks, corruption, and access violations. Memory dump analysis provides insights into how processes interact with virtual memory and whether any issues exist in the management of memory resources.

Identifying Memory Allocation Patterns: Memory dump analysis can reveal patterns of memory allocation and deallocation, helping diagnose memory leaks or inefficient memory usage by processes or applications.

Detecting Invalid Memory Accesses: When analyzing memory dump call stacks, it's essential to consider virtual memory mapping. Invalid memory accesses, such as accessing unallocated or already freed memory, can be detected based on the addresses involved in the crash.

Analyzing Page Faults: If the memory dump analysis shows frequent page faults, it might indicate issues with memory management, excessive paging, or memory pressure on the system.

Identifying Paged Data: Virtual memory management can lead to data being paged in and out of physical memory. Analyzing paged data can help understand the context of the crash and uncover the memory regions involved.

In memory dump analysis, understanding virtual memory concepts is vital for correctly interpreting memory addresses, analyzing data structures, and identifying the source of memory-related problems. It allows analysts to make sense of the memory dump's contents, effectively diagnose issues, and determine whether they are related to physical memory, virtual memory, or a combination of both.

Describe the role of WinDbg and its essential commands in memory dump analysis.

WinDbg is a powerful and widely used debugger provided by Microsoft for analyzing memory dumps, diagnosing system crashes, and troubleshooting complex software and hardware issues on Windows systems. It offers a command-line interface and supports both user-mode and kernel-mode debugging. WinDbg is especially valuable for memory dump analysis because it provides a wide range of commands and features tailored to this task. Here's an overview of WinDbg's role and some essential commands for memory dump analysis:

Role of WinDbg in Memory Dump Analysis:

WinDbg allows analysts to load memory dump files (user-mode or kernel-mode) and perform in-depth analysis to diagnose the root cause of system crashes, application failures, memory leaks, and other issues.
It provides access to call stacks, registers, memory contents, and various debugging extensions that help uncover the sequence of events leading up to the crash.
WinDbg helps interpret bug check codes, identify faulty drivers, examine heap and stack data, analyze threads, and inspect memory corruption issues.

Essential WinDbg Commands for Memory Dump Analysis:

!analyze -v:
Automatically analyzes the memory dump and provides a preliminary summary of the crash, including the bug check code, parameters, and possible causes.

.reload /f:
Refreshes symbol information, allowing WinDbg to access debug symbols related to the operating system, drivers, and modules. Symbols are essential for meaningful analysis.

lm (List Modules):
Lists all loaded modules (drivers and libraries) along with their base addresses, sizes, and symbols.

!process 0 0:
Lists all running processes along with their Process IDs (PIDs) and Parent Process IDs (PPIDs).

!thread:
Displays information about the current threads in the system, including their IDs, states, and stack traces.

!heap -s:
Displays an overview of heap usage, showing the sizes and number of heaps in the process.

!poolused /t:
Displays memory pool usage statistics, categorizing pool usage by pool tag.

!analyze -v:

This command triggers the automated analysis of the crash dump, providing a preliminary summary of the crash, bug check code, parameters, and possible causes.

!peb:
Displays the Process Environment Block (PEB) of the specified process, containing information about process parameters, environment variables, and loaded modules.

!locks:
Displays information about locks held by threads, helping identify potential deadlocks or synchronization issues.

!address -summary:
Provides an overview of memory regions in the process, including the stack, heap, and module addresses.

dt (Display Type):
This command allows you to display the contents of a data structure defined by a specific type. For example, "dt nt!_ETHREAD" displays the contents of the ETHREAD (executive thread) structure.

These are just a few essential WinDbg commands for memory dump analysis. WinDbg offers a vast array of commands and extensions, and the choice of commands depends on the specific analysis goals and the issues being investigated. Developing familiarity with these commands, along with the ability to interpret their output, is crucial for effective memory dump analysis.

How would you approach analyzing a memory dump from a remote system?

Analyzing a memory dump from a remote system involves some additional steps compared to analyzing a local memory dump. Remote memory dump analysis can be useful when you're dealing with a system that's not physically accessible or when you're performing analysis in a controlled environment. Here's how you can approach analyzing a memory dump from a remote system:

Prerequisites:
1. Access to the Remote System: You need administrative access or appropriate privileges on the remote system to collect the memory dump and perform analysis.
2. Network Connectivity: Ensure that the remote system is accessible over the network and that you can establish a connection to it.
3. Debugging Tools: Install the required debugging tools, such as WinDbg, on your local machine.

Steps:

1. Collect the Remote Memory Dump:
On the remote system, generate a memory dump using tools like DebugDiag, ProcDump, or Windows Error Reporting. Ensure that the dump is saved to a location accessible from your local machine.

2. Transfer the Memory Dump to Your Local Machine:
Use secure file transfer methods (e.g., SCP, SMB, FTP) to copy the memory dump from the remote system to your local machine. Make sure to maintain the integrity of the memory dump during the transfer.

3. Open the Memory Dump in WinDbg:
Launch WinDbg on your local machine.
Use the "File" menu to open the memory dump file you transferred from the remote system.

4.Set Symbol File Path:
Configure WinDbg to access symbol files. You can use Microsoft's public symbol servers or provide the path to symbols manually.

5.Set Up Symbol Path for Remote System:
If the memory dump references modules that are not present on your local system, configure the symbol path to include the location of symbols from the remote system.

6.Analyze the Memory Dump:
Use the same memory dump analysis techniques you would use for a local dump. Execute WinDbg commands, inspect call stacks, examine memory contents, and analyze other relevant information.

7. Interpret Results and Diagnose Issues:
Interpret the output of WinDbg commands and analyze the data to diagnose the issues causing the crash or other issues on the remote system.

8. Apply Solutions or Recommendations:
Based on your analysis, develop recommendations or solutions to address the identified issues on the remote system.

9.Report Findings:
Prepare a detailed report of your findings, including the analysis process, identified issues, and recommended actions. Share this report with relevant stakeholders.

10.Repeat and Validate:
If necessary, work collaboratively with administrators or stakeholders on the remote system to implement the recommended solutions. After applying changes, validate the results and verify that the issues are resolved.

Remote memory dump analysis requires coordination and proper access to the remote system, as well as a good understanding of the debugging tools and analysis techniques. Keep in mind that the remote system's configuration, software, and environment may differ from your local machine, so consider these factors while interpreting the results.

What are symbol file and why its important in windbg

Symbol files, often referred to as "symbols," are essential components in the debugging process, and they play a crucial role in tools like WinDbg when analyzing memory dumps or performing live debugging sessions. Symbols are files that contain information about the relationships between source code, compiled binaries, and their corresponding memory addresses in a program or operating system. They provide a bridge between the raw memory addresses present in memory dumps and the actual source code and variable names used during development.

Here's why symbol files are important in WinDbg and other debugging scenarios:

**1. Mapping Addresses to Meaningful Information:
Symbol files contain mappings between memory addresses and their corresponding symbols, which include function names, variable names, structure definitions, and more. Without symbols, raw memory addresses would be challenging to interpret.

**2. Understanding Code Execution and Call Stacks:
Symbols help translate memory addresses in call stacks into human-readable function and module names. This is vital for understanding the sequence of function calls and execution flow leading up to a crash.

**3. Identifying Source Code Locations:
Symbol files allow you to identify the exact source code locations where specific memory addresses were generated. This helps in pinpointing the origin of issues and understanding the context in which they occurred.

**4. Variable and Data Inspection:
With symbols, you can inspect variables and data structures within memory dumps using their actual names. This makes it easier to analyze memory contents and identify potential memory corruption or issues.

**5. Debugging Third-Party Code and System Components:
Symbols are crucial when debugging code that you didn't write, such as operating system components or third-party libraries. Without symbols, understanding and diagnosing issues in these components would be extremely challenging.

**6. Optimized Code and Release Builds:
Symbols also play a role in analyzing optimized and release builds, which might not include full debugging information by default. Symbols enable you to debug these builds effectively.

**7. Minidump and Remote Analysis:
When analyzing minidump files or performing remote analysis, symbols ensure that you can access the relevant information needed to understand the crash context.

**8. Symbol Servers and Version Control:
Symbol servers store and provide access to symbol files associated with different software versions. This is valuable for debugging across various versions of a program.

In WinDbg, you can configure symbol paths to direct the debugger to find the appropriate symbol files. Microsoft's public symbol servers and custom symbol repositories can be used to download the required symbols. By having accurate symbol information, WinDbg can provide meaningful output, such as call stacks, variable names, and function names, that greatly assists in the analysis of memory dumps and debugging sessions.

Security product notes

2023-02-02T01:06:00.002-08:00

What is the best description of a worm?
malware that can independently replicate and spread without human intervention

What are the two words that make up the term "malware"?
malicious and "software"

What are the two words that make up the term "rootkit" and where do they come from?
“Root” refers to privileged access on a Unix operating system and “kit” refers to the various software components that make up the program.

Why are rootkits considered so dangerous?
They can gain and maintain privileged access undetected.

Types of malware

Malware categories include the following:

Worms. A worm is a standalone program that can self-replicate and spread over a network. Unlike a virus, a worm spreads by exploiting a vulnerability in the infected system or through email as an attachment masquerading as a legitimate file. A graduate student created the first worm (the Morris worm) in 1988 as an intellectual exercise. Unfortunately, it replicated itself quickly and soon spread across the internet.
Ransomware. As the name implies, ransomware demands that users pay a ransom—usually in bitcoin or other cryptocurrency—to regain access to their computer. The most recent category of malware is ransomware, which garnered headlines in 2016 and 2017 when ransomware infections encrypted the computer systems of major organizations and thousands of individual users around the globe.
Scareware. Many desktop users have encountered scareware, which attempts to frighten the victim into buying unnecessary software or providing their financial data. Scareware pops up on a user's desktop with flashing images or loud alarms, announcing that the computer has been infected. It usually urges the victim to quickly enter their credit card data and download a fake antivirus program.
Adware and spyware. Adware pushes unwanted advertisements at users and spyware secretly collects information about the user. Spyware may record the websites the user visits, information about the user's computer system and vulnerabilities for a future attack, or the user’s keystrokes. Spyware that records keystrokes is called a keylogger. Keyloggers steal credit card numbers, passwords, account numbers, and other sensitive data simply by logging what the user types.
Fileless malware. Unlike traditional malware, fileless malware does not download code onto a computer, so there is no malware signature for a virus scanner to detect. Instead, fileless malware operates in the computer's memory and may evade detection by hiding in a trusted utility, productivity tool, or security application. An example is Operation RogueRobin, which was uncovered in July 2018. RogueRobin is spread through Microsoft Excel Web Query files that are attached to an email. It causes the computer to run PowerShell command scripts, providing an attacker access to the system. As PowerShell is a trusted part of the Microsoft platform, this attack typically does not trigger a security alert. Some fileless malware is also clickless, so a victim does not need to click on the file to activate it.

What is a PE file?

Portable executable file format is a type of format that is used in Windows (both x86 and x64).

As per Wikipedia, the portable executable (PE) format is a file format for executable, object code, DLLs, FON font files, and core dumps.

The PE file format is a data structure that contains the information necessary for the Windows OS loader to manage the wrapped executable code. Before PE file there was a format called COFF used in Windows NT systems.

Explain Antimalware and antivirus solutions

The four main types of malware detection are:

Signature-based scanning. This is a basic approach that all antimalware programs use, including free ones. Signature-based scanners rely on a database of known virus signatures. The success of the scanner depends on the freshness of the signatures in the database.
Heuristic analysis. This detects viruses by their similarity to related viruses. It examines samples of core code in the malware rather than the entire signature. Heuristic scanning can detect a virus even if it is hidden under additional junk code.
Real-time behavioral monitoring solutions. These seek unexpected actions, such as an application sending gigabytes of data over the network. It blocks the activity and hunts the malware behind it. This approach is helpful in detecting fileless malware.
Sandbox analysis. This moves suspect files to a sandbox or secured environment in order to activate and analyze the file without exposing the rest of the network to potential risk.

What are the Steps of the Cyber Security Kill Chain?

Step 1: Reconnaissance

During the Reconnaissance phase, a malicious actor identifies a target and explores vulnerabilities and weaknesses that can be exploited within the network. As part of this process, the attacker may harvest login credentials or gather other information, such as email addresses, user IDs, physical locations, software applications and operating system details, all of which may be useful in phishing or spoofing attacks

Reconnaissance is the first step in the cyber security kill chain and utilizes many different techniques, tools, and commonly used web browsing features including:

Search engines
Web archives
Public cloud services
Domain name registries
WHOIS command
Packet sniffers (Wireshark, tcpdump, WinDump, etc.)
Network mapping (nmap)
DIG command
Ping
Port scanners (Zenmap, TCP Port Scanner, etc.)

There is a wide range of tools and techniques used by hackers to gather information about their targets, each of which exposes different bits of data that can be used to find doors into your applications, networks, and databases which are increasingly becoming cloud based. It’s important that you secure your sensitive data behind cloud-based SASE defenses, encryption and secure web pages in order to prevent attackers from stumbling on compromising information while browsing through your publicly-accessible assets, including apps and cloud services.

Step 2: Weaponize

Once an attacker has gathered enough information about their target, they’ll choose one or several attack vectors to begin their intrusion into your space. An attack vector is a means for a hacker to gain unauthorized access to your systems and information. Attack vectors range from basic to highly technical, but the thing to keep in mind is that, for hackers, targets are often chosen by assessing cost vs. ROI.

Everything from processing power to time-to-value is a factor that attackers take into account Typical hackers will flow like water to the path of least resistance, which is why it is so important to consider all possible entry points along the attack surface (all of the total points in which you are susceptible to an attack) and harden your security accordingly.

The most common attack vectors include:

Weak or stolen credentials
Remote access services (RDP, SSH, VPNs)
Careless employees
Insider attackers
Poor or no encryption
System misconfiguration
Trust relationships between devices/systems
Phishing (social engineering)
Denial of service attacks
Man-in-the-middle attacks (MITM)
Trojans
SQL injection attacks
And many others

Remember: a hacker only needs one attack vector to be successful. Therefore, your security is only as strong as its weakest point and it’s up to you to discover where those potential attack vectors are. Ransomware attacks continue to exploit remote access services to gain entry, make lateral movements, detect sensitive data for exfiltration, all before encrypting and making ransom requests.

So typically once an attacker is in, their next move is to find different ways to move laterally throughout your network or cloud resources and escalate their access privileges so their attack will gather the most valuable information, and they’ll stay undetected for as long as possible. Preventing this kind of behavior requires adopting “Zero Trust” principles, which, when applied to security and networking architecture, consistently demands reaffirmation of identity as users move from area to area within networks or applications.

Step 3: Delivery

Now that a hacker has gained access to your systems, they’ll have the freedom they need to deliver the payload of whatever they have in store for you (malware, ransomware, spyware, etc.). They’ll set up programs for all kinds of attacks, whether immediate, time-delayed or triggered by a certain action (logic bomb attack). Sometimes these attacks are a one-time move and other times hackers will establish a remote connection to your network that is constantly monitored and managed.

Malware detection with Next Gen SWGs to TLS decrypt and inspect web and cloud traffic are key components for preventing the delivery of these types of payloads. Increasingly attacks are cloud delivered with 68% of malware using cloud delivery versus web delivery. Running inline threat scanning services for web and cloud traffic along with accounting for the status of all endpoint devices is crucial in ensuring your company is not infected with any malicious software.

Step 4: Exploit

Once the attacker’s intended payload is delivered, the exploitation of a system begins, depending on the type of attack. As mentioned before, some attacks are delayed and others are dependent on a specific action taken by the target, known as a logic bomb. These programs sometimes include obfuscation features in order to hide their activity and origin in order to prevent detection.

Once the executable program is triggered, the hacker will be able to begin the attack as planned, which leads us to the next few steps, encompassing different types of exploitations.

Step 5: Installation

Immediately following the Exploitation phase, the malware or other attack vector will be installed on the victim’s system. This is a turning point in the attack lifecycle, as the threat actor has entered the system and can now assume control.

If a hacker sees the opportunity for future attacks, their next move is to install a backdoor for consistent access to the target’s systems. This way they can move in and out of the target’s network without running the risk of detection by reentering through other attack vectors. These kinds of backdoors can be established through rootkits and weak credentials, and so long as their behavior doesn’t throw up any red flags to a security team (such as unusual login times or large data movements), these intrusions can be hard to detect. SASE architecture is uniting security defenses to collect rich metadata on users, devices, apps, data, activity and other attributes to aid investigations and enhance anomaly detection.

Step 6: Command and Control

In Command & Control, the attacker is able to use the malware to assume remote control of a device or identity within the target network. In this stage, the attacker may also work to move laterally throughout the network, expanding their access and establishing more points of entry for the future.

Now that the programs and backdoors are installed, an attacker will take control of systems and execute whatever attack they have in store for you. Any actions taken here are solely for the purpose of maintaining control of their situation with the target, which can take all kinds of forms, such as planting ransomware, spyware, or other means for exfiltrating data in the future.

Unfortunately, once you learn of an intrusion and exfiltration, it is probably too late—the hackers have control of your system. That’s why it’s important to have safeguards that monitor and evaluate data movements for any suspicious activity. A machine is far more likely to detect and prevent malicious behavior faster than any network administrator.

Phase 7: Actions on Objective/Persist

In this stage, the attacker takes steps to carry out their intended goals, which may include data theft, destruction, encryption or exfiltration.

Over time, many information security experts have expanded the kill chain to include an eighth step: Monetization. In this phase, the cybercriminal focuses on deriving income from the attack, be it through some form of ransom to be paid by the victim or selling sensitive information, such as personal data or trade secrets, on the dark web.

Generally speaking, the earlier the organization can stop the threat within the cyber attack lifecycle, the less risk the organization will assume. Attacks that reach the Command and Control phase typically require far more advanced remediation efforts, including in-depth sweeps of the network and endpoints to determine the scale and depth of the attack. As such, organizations should take steps to identify and neutralize threats as early in the lifecycle as possible in order to minimize both the risk of an attack and the cost of resolving an event.

Page Object Model(POM) based Testing using Selenium WebDriver

2022-09-27T03:27:00.003-07:00

Page Object Model(POM) based Testing using Selenium WebDriver

Introduction

Maintaining 1000 lines of code in a single class file is a heavy task and also it increases its complexity. In order to maintain the project structure and efficient performance of the selenium scripts, it is necessary to use different pages for different tasks.

To ease the access of distributing the code into different modules, the Page Object Model(POM) comes to the rescue. In this blog, we will be learning some of the core concepts of Page Object Model(POM).

What is Page Object Model?

Page Object Model is a design pattern which has become popular in test automation for enhancing test maintenance and reducing code duplication. A page object is an object-oriented class that serves as an interface to a page of your AUT.

The tests than use the methods of this page object class whenever they need to interact with the UI of that page. The benefit is that if UI changes for the page, the tests don’t need to be changed, only the code within the page object needs to change.

Subsequently all changes to support that new UI are located in one place so we don’t have to edit much.

How to Implement POM?

Create a New Maven Project

Create a Maven Project so we don’t have to add all jar files into the library which are needed for our project.

It will automatically download and add all the jar files into your project which are required by just adding the dependencies into the POM.xml file of your project.

Advantages of POM

Makes our code cleaner and easy to understand – keeps our tests and element locators separately.
Easy to visualise each step of the scenario, view and edit test cases intuitively.
Test cases become short and optimised as we can reuse page object methods in the POM classes.
Any UI change can easily be implement, update and maintain into the Page Objects and Classes.
Re-usability of code – object repository is independent of test cases.

How to Implement POM?

Create a New Maven Project

Create a Maven Project so we don’t have to add all jar files into the library which are needed for our project.

It will automatically download and add all the jar files into your project which are required by just adding the dependencies into the POM.xml file of your project.

Create a new Package

After the above step create a new package under our project by any desired name of your choice. The package which you are creating is a user-defined package which will create a folder in your workspace.

Create a New Class

After creating the package you have to create a class under the package which you have created in above step. We can also create an object of a class and access it from another class.

Create a Class for Browser

We will create a method while passing parameters with it having driver, browser name and URL of the website.

Under this method we will provide multiple browser options for the user to choose between them and pass the requirement drivers under the specific conditions of the browser.

After above step we will maximise the browser and add ImplicitWait and pageLoadTimeout with it, so if the processor of the system is slow or internet is slow than elements can wait according to the given time.

Than we will pass the url of the website using driver.get(appURL); and in the appURL we will pass the website URL.

Now, we will create a method for browser quit having parameter driver. So when our script is completed than the browser will be quit automatically.

Create a Class for Login Page

We will now create all the elements which are on Login Page using @FindBy so we can directly call them using WebElement. Initialise all the elements together under the class so they can be accessible from anywhere.

Now create a method where all the WebElements of the Login Page will be called to perform some actions. In the method we will pass two parameters for username and password of the website.

Create a Class for Login Page Test

Now we will create another class where all other classes will be called. Before starting of a function we will call @Test which is used to run your script with TestNG.

Create a void method and first call startapplication() method from BrowserFactory class to start the browser while passing parameters which are defined in the method.

Create an object for Login Page with any name and initialise all WebElements using PageFactory. Now call the method where WebElements actions are defined under a method from an object which you have created.

Now, call the method QuitBrowser() from the class BrowserFactory which is used to close the browser after your script.

View of Page Object Model(POM)

Now, if the AUT undergoes any change at the login page or at any page we just need to change the page object. Thus we don’t need to change our test script again and again (even for the new release or built).

The project structure will look like :

Test Automation framework

2022-09-26T07:48:00.000-07:00

A well structure design helps reduce the extra cost and conflicts. We need to develop support libraries for re-usability and expandability of the code in our automation

We have to comment in scripts and function headers which will improve the readability and understand-ability of the structure.

Test automation is the process of automating repetitive processes of users to make the work efficient which saves a lot of time.

What is test automation framework ?

A test automation framework is define as a real or conceptual structure; created to provide support which could expand in future. Test Automation framework is not a single process or tool. It’s a collection of tool and process working together to automate the manual process.

Testing Framework is a set of rules which is used for creating and designing test cases.

Automation Framework is also useful when user want to repeat the same process using test scripts when ever it is required to test on multiple browsers at the same time.

Purpose of a Test Automation Framework

• It improves the design and development of automated test scripts which involves re-usability of components or code.

• Provides a structured development of all test scripts which reduces dependency on individual test-cases which saves time to write the same code.

• Detects issues and bug with proper root causes with minimum human involvement.

• Reduces dependency on teams by automatically selecting the test to execute according to test scenarios.

• Enhance test accuracy and reduces test maintenance cost which involves lower risk of test failure.

• Improves utilization of various resources and enables maximum returns on efforts.

• Ensures an uninterrupted automated testing process with little man-power involvement.

Different Types of Framework used in Automation Testing

Most common types of Test Automation Frameworks are:-

• Linear Scripting Framework: This framework is based on the concept of record and playback mode that is always achieved in a linear manner. Linear Scripting Framework mostly used for testing on the small applications in which step are written in a sequential order.

• Modular Testing Framework: Modular Test Frameworks break down test cases into small modules. There, the modules are independently tested first and then the application is tested as a whole which makes each test independent.

• Data Driven Testing Framework: In this testing framework, a separate file in a tabular format is used to store both the input and expected output results. A driver script where all test cases are called can execute all the test cases with multiple sets of data. This driver script contains navigation that spreads through the program which covers both reading of data files and logging of test status information.

• Keyword Driven Testing Framework: Keyword Driven test framework separates script logic from test data, then stores the data externally. After that, it stores the keywords in a different location. Since user can use the same keyword across different test scripts which re-uses the code.

• Hybrid Testing Framework: A hybrid test framework improves the weaknesses of different test frameworks. It is a combination of many types of end-to-end testing approaches which uses the advantages of other frameworks.

• Test Driven Development Framework (TDD): Test driven development is an approach in which test cases are developed to specify and validate that what will code do. It starts with designing part and develop test cases for small functionalities for your application, which instructs developers to write code if previous script fails.

• Behaviour Driven Development Framework (BDD): This has been derived from the TDD approach and in this method tests are more focused and are based on the system behavior. Testers can create test cases in simple English language which helps even the non-technical people to easily analyze and understand the tests.

Benefits of Test Automation Frameworks

• Optimization of Resources: Test framework helps in making the best use of resources, it does this by making the process easier with use of different resources according to organizational needs.

• Increased Volume of Testing: Test automation frameworks increase the volume of testing by perform test on many devices as it’s not possible to perform manual testing on all devices.

• Simultaneous Testing: Test automation frameworks enable simultaneous testing on different types of devices. When test scripts are automated, than testers can perform the script on other devices at the same time.

• Enhanced Speed and Reliability: Performing different test cases manually can be very time consuming so instead of it we can run all the test cases from our script in very less time.

• More Output in Less Time: An automation script minimises the time taken to prepare and run tests. With increased efficiency and speed, we can gain more output in less time.

• Fixing Bugs at an Early Stage: Test automation framework helps in fixing bugs at an early stage which don’t need much manpower to carry which saves time and expenses of the organisation.

• Remote Testing: With a test automation framework, you don’t need to see all test cases, you can run the test cases and come back later and view the result. User doesn’t need to be present at execution time physically.

• Reusable Automation Code: You can use your automation script in any of your other application or website which has same functionality which increase the code re-usability.

Steps for an Effective Test Automation Approach

• Evaluate to understand real need for automation based on Website/Application type: We should first evaluate what need to be automated which saves the time of the user which he losses it by doing it manually.

• Define automation goals and priorities: The Goals should be first set so we can move ahead in that direction to make the test script and achieve it while having priorities to automate.

• Plan automated testing strategy: Automated Testing Strategy should be planned so that test cases should be built accordingly.

• Select right automation testing tool & testing framework based on your project requirements: The Testing tools & testing framework should be selected before automating the manual process so the script which we are making should be constructed in a proper way with right tool.

• Decide which test case to automate: We should know which test case need to be automated because it can save the time of the user which he spends doing it manually.

• Develop good quality of test data: The script which you are creating should be of good quality which can be used later also and the data which it produces as a result should be in readable format.

• Create automated tests which are more stable to UI changes: Automated Tests which are created should be stable enough even if there are some minor changes in the UI than also your script is able to run the test.

• Execute tests for test scripts developed: Test Scripts which are developed should be executed so the result can be known whether it is correct or not and we can check whether the script which we have created is stable enough or not.

• Test early and often with continuous integration and continuous delivery (CI/CD) pattern: We can test our script early with Continuous Integration and Continuous Delivery that whether the script which we have created is good enough or not.

• Maintain test scripts for future use: Test Script which you have created should always be kept for the future use so you don’t have to write the same code again and again, which you can reuse the code of the script which is required in your new script.

Common Misconceptions about Automated Testing

• Automation will provide you with more free time: The misconception that automation will provide you more free time is both true and false. In manual testing, most of the time is devoted to explore and do functional testing where we manually search for errors.

With automated testing, that time is cut drastically. The work for automation testers is instead spend in coding the test script and making improvements to tests repeatedly as adjustments are needed.

• The Cost of Automated Testing is Too High: Investment in automated testing might feel costly, especially for a smaller company. But according to report, over time, automated testing pays for itself.

Automation testing also reduces the cost for multiple code revisions, over the course of time, the investment pays out. Manually repeating these tests is costly and time-consuming; but automated tests can be run over and over again at no additional cost.

• Automated Testing is better than Manual Testing: There is no superiority in the automation vs manual; they are just “different”. Manual testing is performed by a human sitting in-front of a computer carefully going through application; trying various input combinations, comparing the results to the expected behavior and recording the results.

Automated testing is often used after the initial software has been developed. Lengthy tests that are often avoided during manual testing can be automated to save the time. They can even be run on multiple computers with different configurations.

• Automated Testing Inhibits Human Interaction: Automated testing is more clear-cut and faster than what humans could do with less human errors, so this misconception is understandable.

Automation testing do not replace face-to-face communication which is a necessary part of a software development. Instead, it increases the aspect by providing another channel through which to communicate.

Important points consider while Designing Test Automation Framework

• Handle Scripts and Data separately – Automated test scripts should be separated from input data files (eg – XML, Ms-Excel or Databases) and code, so that no modifications are needed to the test scripts whenever some data has to be changed.

• Library – Library should contain all reusable functions such as databases, generic functions, application functions etc. so that we have to just call the function rather than writing the whole code again and again.

• Coding Standards – Coding standards should always be maintained across your test automation framework, which will encourage individual coding practices and help in maintaining code structure, which makes it easier for others to understand the code.

• Extensibility and Maintenance – An ideal test automation framework should regularly support all new updation to the software application which allows modification. e.g. Some new library can be created, which would help in updating application features with less effort.

• Script/Framework Versioning – Versions of your Test Automation Framework / scripts should be maintain in a local repository or some versioning tool, which would help in easy checking of changes to the software code.

Goals for designing a Test Automation Framework

The framework design should be easy to expand and maintain
Provide abstraction from complexities
Identification of the common functions used across scripts
Separate complex logic functions with utility functions
Separate test data and test scripts
Creation of robust functions
Appropriate functional break down which can be changed
Ensure scripts are executed without human intervention, even in false conditions
Improve Design documentation

Using Page Object Model in Test Automation Framework

You need classes that interact with the pages of your website. These classes should be within the framework layer. The most popular design pattern for creating these types of classes is the page object model (POM). This model recommends creating a separate class for each page of your website, (e.g. buttons, text fields, etc), as well as methods for interacting with those elements. You can use a browser automation tool, such as Selenium WebDriver, to handle the actual interaction.

The role of Inheritance in Test Automation Framework

Inheritance, an object-oriented programming principle that enables objects to receive properties from a parent object, also has its place in your automation test code.

We have to always launch the browser for running our scripts. Rather than duplicating your code in every test method, you can use this functionality, and place into a method that runs before each test. To verify, this method does not get duplicate in every test class, place this method in a base test class from which all test classes inherit. The base page can also contain objects for other parts of the website that are visible from any page, such as navigation menus, headers, and footers. All of these would be inherit by any page, and therefore accessible without duplicating code.

Test runner tools, such as JUnit and TestNG, provide “before” annotations that you can use to denote methods that should run before the test. They also provide “after” annotations that you can use and can be inherit in the same way to clean up after tests.

How To Design a Test Automation Framework

Some points which should be consider while designing a framework:-

Create Wrapper Method: Writing a wrapper method is one of the solutions for extending the library features. An example of extending the wrapper method is to allow better logging capabilities and handling the errors well in Selenium.
Implement Custom Logger: While running the test script; all information should be logged into the file. This information can be use as a reference for understanding the code. The popular logging framework for java is log4j and python is Custom logger.
Choosing the Right Design Pattern: Choosing the right design pattern speeds up the test case development and helps in preventing minor issues that can cause major problems and therefore improves code readability. The most popular design pattern for creating a selenium automation framework is the Page Object Model (POM).
Separate Tests From Automation Framework: Separate the Test script logic and the input data from the automation framework. It increases code readability and makes the code readable.
Create a Proper Folder Structure For The Code: Always define the folder structure which makes the code readable and makes it easy to understand. Eg – Test Cases, Utilities, Input Data etc.
Build & Continuous Integration: Continuous Integration is a development practice that integrates with a build automation tool like Maven to ensure whether the software is running without any breaks after making a commit decision.

Software Testing/ QA

2022-05-02T02:41:00.005-07:00

What is quality assurance?

The role of QA exists to prevent problems in an application so that users don't encounter bugs and crashes. Quality Assurance, referred to simply as QA, is a systematic process used to determine whether a product meets specifications. An individual in this role can have many titles including QA, QA engineer or QA analyst, Software engineer in test, or Tester. Throughout this course, you will hear me use these titles interchangeably. An individual in the QA role constantly questions parts of the software development process to ensure the team is building the right product and building it correctly. A QA's primary goal should be to help their team move quickly with confidence. They establish and maintain standards for how to best test a software product. Having solid software testing practices is a huge asset to any team in order to produce a well functioning application.

How to ensure quality

Good quality results in a software product that is built correctly, as specified, and works reliably. Quality can be ensured across the code and influenced by process. It can be measured in various ways. Perhaps by customer happiness, annual revenue, or how well the application functions over time. Every quality software product has a team behind it that's responsible for its success. The team is composed of multiple roles. It is up to all of them to work together to produce high-quality software. It starts by having clear specifications. Then the specifications can be implemented in code, and the code is tested thoroughly to ensure the application works as intended. After the code is released, users will start to use the application and provide feedback. There isn't a quick and easy solution for how to ensure quality. Instead, it's an ongoing process that the whole team needs to be invested in. And to maintain quality, it's necessary to continue to iterate and improve on processes in order to have the best working software.

Role of QA

1) Get involved throughout the SDLC

The software development lifecycle, referred to as the SDLC, is a process that processes high-quality software in the shortest amount of time. The SDLC includes detailed steps for how to effectively develop, change, and maintain a software system, and is typically broken down into six parts: The steps are linear and do go in a sequential order, but what's more important to understand is that it's a cycle that each feature should iterate through. Traditionally, a QA has only gotten involved during the testing phase, but it's proven really useful for a tester to get involved as early and as often as they can to ensure quality throughout the entire development process. During the planning phase, or identify use cases of the feature. how to best mitigate risk or look for alternate solutions. When defining a feature, a QA can help write specifications or acceptance criteria and help decide what's in scope and what's out of scope. At this phase, a QA can also begin to write a test strategy and test scenarios. And also here the team can define when the product will be released and what metrics can be used to measure success. In the design and build phases, a QA can solidify test scenarios and get feedback on them from the team. They can begin to manually test the scenarios defined and script automated test as well. In the test phase, manual and automated tests are completed. This usually happens with the help and collaboration of developers. A QA can also work with a business team member to determine if the functionality will be accepted into the release. When it's time to do the deploy of the product, a QA is usually involved in the release process and helps to validate the release build. After the release, a QA will verify the functionality in production is still working as expected. or one development sprint, the same cycle can start all over again in another iteration. By getting involved outside of just the testing phase, By getting involved outside of just the testing phase, the product will have quality built into it at all stages. the product will have quality built into it at all stages. This will ensure a successful release This will ensure a successful release and a great experience for users. and a great experience for users.

2) Collaborate with the team

It is so valuable to collaborate with cross-functional teammates in each of the phases of the SDLC. Collaboration between teammates leads to a better understanding of each others' roles and a better outcome for the product. and in return help others develop a quality mindset. In a typical software delivery team, there are developers, designer, a tester, and product manager or business analyst. The team works together throughout the SDLC to deliver a quality product. get involved within different phases. The plan, define, and design phase can include a representative from each role. The build and test phase includes a developer, a tester, and a designer. The deploy phase includes a developer, a tester, and a product manager usually has the final sign off. A QA typically collaborates with a business team member to help determine acceptance criteria and scope for a future or story. A business team member can also work with QA to provide sign off on stories and get feedback about test scenarios and what to automate. When working with design, a QA provides feedback on mocks, prototypes, or the product itself after it has been deployed. Developers and QAs pair together to write test and validate functionality. Typically, the more collaboration, the better. Get creative and find the best ways to collaborate with your teammates across different phases of the SDLC. This will allow a QA to get more insight on how to do thorough testing, and will keep a team more in sync by creating a shared vision by creating a shared vision by building trust and accountability. by building trust and accountability.

3) Set expectations and goals

I have shared how varied the role of a QA can be. Keeping that in mind, when you join any new team or project, it will be necessary to set clear expectations, and measurable goals. It's important to ask questions, to understand your role, share your strengths, and identify areas in which you want to grow. This way, you will come into a situation being fully aware of what to expect. It's also important to build a relationship with the team. Get to know each of your teammates, their role, and build trust with one another. Spend time collaborating, and also schedule time for one-on-one sessions. Some individuals may have never worked with a software tester before. Some have a misunderstanding about how the role works, and what it entails. Getting to know your teammates will spark ideas about how to best collaborate cross-functionally, and support one another. will make you more accountable, because others will be aware of your goals, and can help you to achieve them. As you get up to speed, and start contributing to the project, make sure to regularly check in with your teammates. Constantly communicate what you are working on to the rest of the team, and don't be afraid to speak up if you see something wrong. If you need help, find someone who can answer your questions. Over time, ask for feedback to understand if you are meeting expectations, and give others feedback about your experience has been working with them. Always try to give candid feedback, and align the feedback with how an individual is meeting up to their goals. When I was a consultant, I had the opportunity to work with many different clients with unique needs. It was necessary that I be able to set clear expectations with my team early on, especially if I was only going to be working on a project for a few months, and didn't want to waste any time getting off on the right foot. Before starting a project, I tried to get as much information as I could, by talking to the team and understanding their challenges. Then I would take some time to observe and assess the situation. That allowed me to see first-hand what would work best for that project, and which skills I would need to apply to make a change. Once I had a clear plan of approach for testing, I shared that with the team, With that said, I would get to work to collaborate with the team, to fix some of the challenges Every few weeks or so going forward, and see what I was doing well, and how I could improve. If you're not already doing any of this, I would recommend starting now. In addition, one-on-one meetings, or retrospective sessions, are great opportunities to share feedback, and talk about how well expectations are being met. If you want to be a successful QA, If you want to be a successful QA, then setting expectations, then setting expectations, and checking in on them regularly, and checking in on them regularly, will give you a great start. will give you a great start.

Test Planning

1) Create a test strategy

For each project, a QA engineer will create a test strategy, which describes how a product will be tested. A test strategy is useful so that anyone can read and understand the scope of testing clearly. I'll walk through a template to show what details I include in a test strategy. This template can be reused and modified for any project. First up is the introduction. The introduction is a high-level summary of the project. An example introduction can be, this strategy outlines what quality provides to the project, what type of testing is done, and how testing is carried out. The aim is to ensure quality in all phases of the development lifecycle to deliver a great experience for our users. Next up are references. This will include any relevant links for their project, including their project's repository and tools used in the tech stack. As an example here, and describe the application teck stack and tools being used for testing. Next up is QA deliverables. This is what a QA engineer will provide to the team. The first deliverable is this quality strategy, the high-level guide of how quality will be maintained on our project. Next there are test plans for each feature which lists test scenarios. Then there are issues reported. Examples of issues reported include bugs, enhancements, and usability improvements. Another deliverable is a release process document. This describes the steps to do a release to production. Moving along in the test strategy, there is the test management section to describe what resources are needed to carry out testing. First up is tooling. An example of tooling is, Jenkins is used to build test versions of the application and virtual machines are used to test the application in Windows. Then there are test environments which describe what environments are needed for exploratory and manual testing. An example of test environments is that manual testing will be done in environments created on-demand. Automation testing is run against a dedicated machine and across Mac and Windows using Chrome. Then, there are supported platforms and versions. For example, Mac and Windows are the supported platforms and each major browser is tested against them. Lastly in this section is test data. A simple example of test data that will be needed is test accounts to access the application. Here it can be helpful to create a table of accounts so that they can be referenced later when testing. is the scope of testing. This describes what types of tests exist for this project. Examples of test include unit, integration, functional, regression, and so on. For each test type use, specify how many there are or how much of the code they cover. Also identify which tools are used to write each type and who owns them. Those five sections in the test strategy do a good job at setting expectations for what a QA will provide, what resources are needed, how testing will be carried out, and which test will be performed. I'll include the test strategy as a handout for this video. Work with your team to create Work with your team to create a test strategy document for your project. a test strategy document for your project.

2) Make a test plan

- Each feature should have an associated test plan. and edge case scenarios to describe how a feature should function, examining it from many angles. During the definition phase, a QA engineer will start to create a test plan for the feature. This way there is ample time for it to be completed, reviewed, and executed before the test plan is over. The test plans I create have four main parts. First there is the scenario, which explains the steps or action that will be executed. Then there is the expected result, which describes what the outcome will be for a given action. Next there is the latest result, and last, there is a field for whether or not the scenario will be automated. This will either be true or false. There is one unique scenario per row. Let's go through an example now. Say I'm working on a new feature for user management. This feature provides the ability to add and delete users, or edit a user's profile. If I focus on each of these user management areas, I can brainstorm a long list of scenarios. I'll first dive into defining scenarios for adding a user. Say I want to click a button to add a new user. Once I click, the expected result will be that the create user modal opens and has two required fields for username and email. There is a create user button that becomes enabled once the fields are populated. After the feature is implemented, I'll check if this passes or fails based on the expected result. It's likely that each scenario will be checked multiple times or by different individuals. So every time the check is done, the latest result can be updated. The last part of the scenario is whether it should be automated. Adding a new user sounds like an important feature, and likely something we're going to want to know always works. Therefore, this is a good candidate for automation. After defining one scenario, I can move onto other scenarios for adding a user, and then editing and deleting users. Once a test plan is complete, I end up with anywhere from 10 to 100 scenarios. The number doesn't really matter so much. What's more important is that the test plan identifies all the possible actions the user can take when using a feature. When a test plan is complete, have a review meeting Send out the test plan to attendees to asynchronously read through the scenarios and identify gaps or fill uncertainties. Once all the feedback has been addressed and the test plan is solidified, it can then be referred to later when testing individual components or stories of the feature as they become complete. In addition to reviewing the test plan as a group, I've seen great success when a team does group or mob testing together for 30 minutes to run through each scenario in the test plan. This happens in advance of the release and can give team members the chance to use the feature across different browsers, platforms, or devices. across different browsers, platforms, or devices. A test plan is a living document that should be updated A test plan is a living document that should be updated as scenarios change and as tests are executed. as scenarios change and as tests are executed. It is a valuable artifact to have for every feature It is a valuable artifact to have for every feature of an application. of an application.

3) Write acceptance criteria

- It can be difficult to take a feature and determine how to implement it as a whole. User stories help break down a feature into manageable sized pieces of functionality. They typically have acceptance criteria which specify what work is included as part of that particular slice of the feature. Acceptance criteria or AC for short are conditions that a software product must satisfy to be accepted by a stakeholder. Acceptance criteria clearly define how each feature should look and function in detail. They're an extension of scenarios to find and test plans. An acceptance criteria allow a developer to know what to implement code for, a business analyst to know what scope the story covers and a QA to know which scenarios to test. Acceptance criteria follow a specific format. They always start with a given. This is a precondition or beginning state Next is the when. This describes the input or action of the scenario. The final part is the then. This describes the expected outcome of the scenario. Let's look at an example of a user story which will provide the functionality to add an item to a shopping cart. One scenario of acceptance criteria might be given I am viewing an item, when I press the Add to Cart button, then the item is added to the cart. Other acceptance criteria might define an error scenario. Let's take a for example adding an item to a cart that is sold out. Given I am viewing an item that is sold out, when I press the Add to Cart button, then the item is not added to the cart. And I see a message that the item is out of stock. In this acceptance criteria I also add an and statement to describe an additional expected outcome for this scenario. This can be done for any part of the acceptance criteria. it's pretty straightforward to define an acceptance criteria especially if scenarios have already been defined in a test plan. This is just another way to ensure quality and know that an application and know that an application is being built exactly as specified. is being built exactly as specified.

4) Identify when testing is complete

It can take some time to work through all the activities within each phase of the software delivery life cycle. At some points of the SDLC, it can be unclear to know when you have done enough to move onto the next phase. This is definitely true for the testing phase. To take ambiguity out of the equation, it helps to determine what steps need to be taken to say that each story has been adequately tested. To do this, you need to define what it means for work to be done. The definition of done will specify what actions need to be completed before a piece of functionality is ready to be released to the public. The team should decide what will be included in a definition of done, so that they have a shared understanding and abide by it. Typically, this definition includes manual of the acceptance criteria from product, design, and QA. Work will start moving fast on projects and it can be easy to cut corners when the team is in a rush and trying to get work completed before a release. There have been countless times when a release deadline is fastly approaching and teammates have tried to rush me through the testing phase by suggesting things like delaying automation until after the release. When a standard is setup, the team is held accountable to follow the steps for each story to get proper sign off. While having an explicit definition of done might sound like a lot to do for every user story, it's just one final step to add some extra confidence. Since there were test scenarios, an acceptance criteria defined and testing throughout the process, After all, it's better to spend a little extra time making sure things are right making sure things are right than rushing to fix a nasty bug that's discovered too late. than rushing to fix a nasty bug that's discovered too late.

Types of testing QA

Box testing

One way to model testing is to think about it in terms of a box. that can be performed so that there is a holistic approach to testing an application. First, there is black box testing, which means that the box is completely concealed and it is not possible to see inside of it. Each test scenario here examines the product from the outside. It allows input to the box and gets output from the box. This means that there is no knowledge needed about the internals of the application, such as what the source code is doing or how the system is working. The focus with black box testing is to perform an action in the user interface and expect a certain result from that action. Black box tests include manual testing and UI automation testing, both of which will help uncover issues with functionality and usability. QA engineers are responsible for this level of testing. Next up is gray box testing. Here the box is semi-transparent. Test scenarios here examine the interaction between the outside and inside of the box. It requires QA engineers to have a deeper understanding of the application. Gray box tests include integration testing, which examines how components of the application work together. They can trigger some action in the UI and see how the code responds. Typically QA engineers and developers are responsible for these level of test. And lastly, there is white box testing. Here the box is completely transparent and focuses on the internals of the application and what is happening at the code or system level. It tests specific functionalities in the code and verifies the result. White box testing includes unit and system testing. Developers are responsible for these type of tests and write them alongside development. Take for example a shopping cart on an e-commerce web application, items can be added and removed from the shopping cart and a total is displayed based on the quantity of items in the cart. For this feature I'll want to think about the type of testing that can be done to ensure quality and confidence that the application works as expected. At the white box level of testing I'm starting from inside the box. Examples of test scenarios here that can be executed at this level are that the quantity can be increased and decreased successfully, and the calculation of items is performed correctly. These tests are written by calling functions in the code that can increase, decrease and calculate the total. Different values are provided to the functions and expect an exact result to be returned. At the gray box level of testing and the results a server or database returned. I want to know that the box as a whole works well rather than one specific component. A test at this level I might write would be to add an item to the cart and confirm form the API response that the item was added and the cart price was updated. Tests here start from the client, which sends a request to the server, and the server responds with details which I can verify. For black box testing in this example I'm focusing on what input I provide to the box and what output I receive. An example of a test here is to add an item to the cart using the UI and see the cart quantity and price update. To write this level of test I manipulate web elements in a browser to click and add items to the cart and navigate to the cart. I can also get the value of web elements and confirm the output is what I expect. and confirm the output is what I expect. So that's how you can model testing as a box. The whole idea is about looking at a box, The whole idea is about looking at a box, or whatever application is under test from multiple angles to provide thorough test coverage. from multiple angles to provide thorough test coverage.

Manual testing

Manual testing follows the steps as a user performing workflows in the application. The goal is to uncover any issues in the functionality and usability. Before performing manual testing know what scenarios you want to cover. You will have to understand your customers and identify both their typical and nontypical use cases. Testing at this level is done in the test phase Manual testing is a type of black box testing. Let's look at an example for an airline site where customers search and buy flights or check their flight status. I will focus specifically on the feature for searching for flights. First, I'll take some time to brainstorm scenarios that an user can perform while searching for flights. All the scenarios I brainstorm will be added to a test plan for this feature. I'll think about the Happy Path Scenarios which are scenarios that have successful results. This includes searching for valid one-way flights and round-trip flights and getting a list of flights available. Then I'll think about Sad Path Scenarios which are scenarios that return errors or do not have results. This includes scenarios such as searching for the same city and destination, searching for invalid routes, and searching for routes that do not operate on certain days. Then I'll write down scenarios into a test plan spreadsheet specifying the scenario and expected result. Here I can even get down to a more granular level for the scenario by specifying the origin airport, destination airport, departure date, and return date. I can use this test data to execute the test scenarios. This isn't necessary but can be helpful so that there are specific examples of data to see the results of the scenarios. Having this granular level of data is especially helpful for automation, which we will take a closer look at later. Once a feature is ready to be tested, I will refer back to my plan to manually test each scenario specified and mark whether they passed or failed in the latest result column. Any failing scenarios will need to be addressed and fixed before the feature will be considered done and ready for release. and ready for release.

UI automation testing

- UI automation is like manual testing but uses a script to automate test scenarios. The benefit of UI automation is that scenarios can be executed repeatedly by running a test script. This will help catch regressions and other oddities much quicker than when done manually. Another benefit is that the scripts can be run on any platform or browser, which is great because it will emulate the interactions of users and their platforms and browser combinations. UI automation tests can be started in the build phase of the SDLC and then completed after the functionality has been developed during the test phase. It is a type of black box testing because it provides input to the UI of an application and expects particular data returned as a result. To get started I refer to the test plan for the feature at hand and determine which scenarios will be automated. I recommend only automating the most important workflows and not every single scenario, taking anywhere from a few seconds and up to a minute to complete. As the test project will continue to grow over time the more UI automation that exists the longer it will take to execute all the scenarios. Looking at the test plan for the flight search feature I'll decide to automate the first three scenarios, because if any of these fail I can assume in automating the sad path cases. After deciding what to automate I will start writing a test script to search for flights. Each scenario will be one test. And in each test I will write code to drive action in my browser by simulating entering flight data including origin, destination and flight date. I can then send actions to the browser, depress the search button, Luckily I already have some sample routes I've defined in my test plan, and I will use the same city data and trip dates in my automation test as well. Once the test script is complete make sure it runs reliably and runs often make sure it runs reliably and runs often so that any irregularities in the applications interface so that any irregularities in the applications interface can be caught and corrected. can be caught and corrected.

Integration testing

- With the surface level of the application tested by manual and UI automation, a QA engineer might want to move on to test the application from another perspective. Integration testing focuses on the interaction between components at lower layers of the application. This level of testing covers similar scenarios as we've seen with manual and UI automation testing, but doesn't look at what's happening at the UI level as a result. Instead, integration tests see how the system reacts to certain actions. Integration tests have some knowledge of how the system works internally, and because of that they are a type of gray box testing. QAs or developers usually write these tests during the build and test phase. Take for example the scenario of searching for a one way flight. Here we can send a request to search for a flight providing the flight parameters to the server directly instead of performing the action from the UI. We'll then wait for the server to send a response to the request and can confirm that the API returns information we expect, such as a successful This type of integration tests the interaction between the application and the server to confirm that the right information is sent and received. If the request returns the wrong status code, or other incorrect flight data, we know that there is a problem with the flight search feature. The benefits are it can catch issues with functionality and can be run in a matter of seconds, meaning we can write more integration tests than UI automation. QA engineers should gain familiarity with integration testing and look for opportunities to implement it for each application feature. to implement it for each application feature.

Performance testing

- Performance testing is done to benchmark how a system performs under load. It will help ensure that an application can scale over time and use. because we test how the system operates under certain stress but don't have visibility into what's going on inside the system. While manual, UI automation, and integration testing are the most common for software projects, performance testing is also very valuable. There are a few different types of performance testing Load testing checks the application's ability to perform under anticipated user loads. The objective is to identify the maximum operating capacity of an application by observing when bottlenecks occur. If I focus on the Search Flights feature, this sends a request to look for flights and returns all results found. I'll want to set up a test to simulate many users simultaneously searching for flights. I can use software that generates thousands of different sessions of flight searches. While the system is under load, I'll want to monitor how long the requests take to complete, and identify when spikes or points of long load time, start to occur in the application. There is also endurance testing. Endurance testing, sometimes referred to as soak testing, is done to make sure the application can handle the expected load over a long period of time. This involves simulating many flight search requests and monitoring the system to see if performance degrades. The goal of endurance testing is to check for system problems such as memory leaks. It is similar to load testing but lasts much longer and monitors unusual behavior that can occur in the application or database. And then there is stress testing. Stress testing involves testing an application

Security testing

- As you know, people don't always use the internet for good. or find ways to bring applications down. Security testing is performed to reveal flaws or vulnerabilities that can be exposed by users. Manual UI automation, an integration test, focus more on functionality and confirming it works as expected. Security testing instead looks to expose problems in the application that can either cause it to behave in unexpected ways or stop it from working. Potential problems can include loss of customer data and trust, decline in revenue, and website downtime. There are so many different ways to approach security testing because they are so many ways someone could try to hack an application. SQL Injection is one of the most common types of attacks used by hackers to insert SQL database statements into any text field. This can expose critical information and allow the system to be manipulated. Thinking about the search flight feature, I could use SQL Injection on different fields in the search flight page and try to inject data that will manipulate flight data. I'll want to test where SQL can be injected I'll validate the values received before passing the query to the database. Another common and harmful type of attack This type of attack tries to take down making it inaccessible to users. In terms of flight search, it can be possible to use bots to flood the server with traffic, searching for a large number of flights, or try to send information that will crash a server. To stop a DoS attack, tools can be used to identify requests that are likely coming from bots and eliminate that traffic.

Bug Reporting

Identify bugs

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- When an application is built perfectly, there will be no bugs. But as we know, humans are error-prone, and there's no such thing as a perfect software application. Bugs are inevitable. They occur when the system does not work as designed or specified, and result in incorrect or unexpected behavior in an application. when Grace Hopper was working on a relay calculator and operations were not completing because a moth was physically stuck in the computer. Removing the moth fixed the problems and operations started completing successfully again. Examples of bugs can be when a vending machine gives the wrong item. Perhaps I selected A5 but the item from B5 was dispensed instead. Or even worse, nothing dispenses at all. Another example of a bug can be when an ecommerce website does not calculate the right sales tax or total. Bugs are versatile. They can be low impact or high impact, they can affect many users or just a handful of users, they can be constantly reproducible or not, and some bugs even go away and come back later. The only constant with bugs It will be necessary to determine how to manage bugs for a project how to manage bugs for a project so that the application can continue to run smoothly. so that the application can continue to run smoothly.

Report bugs

- Once a bug is identified it should be reported right away. Use the reporting system to create and manage bug reports. Bug reporting systems make it easy to do things like report, triage, view, assign, and close bugs. There are an abundance of options available. Some focus specifically on bug management while others provide a variety of services to manage a software project. Some popular options include Jira, Rally, GitHub, and Bugzilla to name a few. I recommend managing bugs within the same software you use to manage your project. Otherwise pick a tool specifically for bugs if that suits your needs best. For example, if your team uses Jira to track features, user stories, and tasks, then bugs can be tracked there as well. With Jira, there are many attributes that can not only describe the bug but also assign a priority, status, or owner to the issue. Other systems like GitHub have fewer attributes but allow you to put an abundance of information in the description using markdown to style the body, and allow labels to be attached to the bug to provide extra information. All bug reporting systems are different. At a minimum, they allow reporters to thoroughly describe the bug. It's also beneficial to be able to categorize bugs so that they become easy to find and analyze. Choose a bug reporting system to accurately report and manage bugs. When reporting bugs, it's necessary to report details about the bug and any other details that will be helpful when reviewing and fixing the bug. A bug report should include details like the name of the bug, a description with steps to reproduce it, an expected and actual result, a picture, video or screen shot, the browser or software version, and a log when applicable. Let's look at an example bug report for an eCommerce application where items are not added to the cart The steps to reproduce are to go to the application home page and select first item and choose add to cart. The expected result is that when I go to the cart, I can see the item that I selected has been added. The actual result is that when I go to the cart there are no items. I'll also record and include a GIF which clearly shows the steps to reproduce the bug and see the problem. And then I'll check in my browser console to see if there were any helpful logs I can find and attach. Lastly, I'll tag an individual or team to look into the bug, give it a priority of high, and a status of ready for development. so that all fields are presented to the bug reporter to provide thorough detail about the issue they found. This makes all bug reports follow a similar structure This makes all bug reports follow a similar structure with enough information for anyone with enough information for anyone who reads the report to understand. who reads the report to understand.

Triage bugs

- You will want to regularly go through and review open bugs with representatives from development, business, and QA. Start with and prioritize bugs and identify the severity and priority of each one. Severity is based on how impactful the bug is to the business, and priority is based on how fast the bug should be fixed. Let me show you what this looks like so you can better visualize it. Severity and priority can be plotted on a basic graph. Let severity be on the x-axis and priority on the y-axis. In the lower left hand quadrant, there is low severity and low priority. These types of bugs only affect a minimal amount of customers and don't affect major workflows. This level of bug isn't very impactful. In the upper left hand quadrant, there's low severity and high priority. Bugs here are important to fix, While the bug might be very visible, it is not preventing users from completing any workflow. For example, on an e-commerce site, during the checkout, there might be a glaring UI bug that breaks some HTML. While it is distracting, it is not preventing users from purchasing items. In the lower right hand quadrant, there is high severity and low priority. Bugs here cause major problems, but only under some circumstances. using an outdated operating system such as Windows 7, In the upper right hand quadrant, there is high severity and high priority. Bugs here are major problems that affect most customers. Bugs at this level indicate service disruption and cause the application to be unusable in some workflows. For example, perhaps users are unable to purchase any items. This is frustrating for users and equally frustrating for the business because they can't make any money. Using this matrix will help decide how to best order bugs to be fixed. You can then classify bugs as level one through four, or high, medium, low. After all new bugs are prioritized, you can get to work on fixing them in order of importance, you can get to work on fixing them in order of importance, and don't forget to set up and don't forget to set up a regularly occurring meeting to triage bugs. a regularly occurring meeting to triage bugs.

Communicate bugs to the team

- After bugs have been prioritized, communicate details about the status of bugs with the team. Share things like the top priority bugs, Listen to the team to reach consensus that bugs have been prioritized correctly. Clarify the effort and time it will take to fix bugs, and identify who will be able to fix them. To communicate the status of bugs, it can also be nice to have a bug specific project board. The project board can include columns for new, ready for development, in progress, QA, and done. Place box in the appropriate column and keep the status updated. You can also capture analytics about your bugs such as the amount open and closed per month. This can give you an idea of how frequently bugs are being fixed in relation to how many are being created. Identify the features where bugs are coming from. This can be good to see where bugs are occurring in the application and if there are any trends. Communicating bugs to the team will let the team know that it's important to acknowledge and fix bugs regularly. to acknowledge and fix bugs regularly.

Communicate bugs to the team

Have bug bashes

- It's important for your team to dedicate time to both find and fix bugs. To find bugs, it can be great to have mob testing sessions around particular features in the application. Taking one hour, have a group of teammates get together to test. They can either do exploratory testing of a specific feature to help uncover bugs, or they can do manual testing using a test plan. This method is a bit more guided, and expects testing to follow the defined steps and scenarios. I recommend doing mob testing at least one week before the release date for every major feature, so your team has time to fix any identified issues. Outside of development sprints, have a bug bash. A week where team-members focus entirely on fixing bugs. This allows individuals who don't always fix bugs to dig deeper into the codebase. I recommend having bug bashes two to four times a year. They can be great for your application's health, and fun for your team.

Learn SQL in 20 days

2022-04-13T03:21:00.011-07:00

DAY 1

SQL ( STRUCTURED QUERY LANGUAGE )

DATABASE

What is DATA ?

"Data is a raw-fact which describes the attributes of an Entity ".

Properties or Attributes

DATABASE : "Database is a place or a medium in which we store the data in a Systematic and organized manner "

The basic operations that can be performed on a database are

▪ CREATE / INSERT

▪ READ / RETRIEVE

▪ UPDATE / MODIFY

▪ DELETE / DROP

These operations are referred as "CRUD" Operations .

DATABASE MANAGEMENT SYSTEM ( DBMS ) :

"It is a software which is used to maintain and manage The database "

▪ Security and authorization are the two important features that DBMS provides .

▪ We use query language to communicate or interact with DBMS

▪ DBMS stores the data in the form of files .

RELATIONAL DATABASE MANAGEMENT SYSTEM (RDBMS ):

"It is a type of DBMS software in which we store the data. In the form of Tables ( rows & columns ) ".

• We use SQL to communicate or interact with RDBMS

• RDBMS stores the data in the form of Tables.

RELATIONAL MODEL :

Relational Model was designed by E.F CODD .

In Relational Model we can store the data in the from of tables .

Any DBMS which follows Relational Model becomes RDBMS .

Any DBMS which follows rules of EF CODD becomes RDBMS .

TABLE : "It is a logical organization of data which consists of Columns &Rows .

RULES OF E.F CODD :

1. The data entered into a cell must always be a single valued data .

2. According to E.F CODD we can store the data in Multiple Tables , If needed we can establish a connection between the tables with the Help of Key Attribute .

3. In RDBMS we store everything in the from of tables including

Metadata .

Example : Metadata : The details about a data is knows as Metadata.

4. The data entered into the table can be validated in 2 steps .

By assigning Datatypes .
By assigning Constraints .

Datatypes are mandatory , whereas Constraints are Optional .

DATATYPES :

It is used to specify or determine the type of data that will be stored In a particular memory location .

Datatypes in SQL :

1. 1. CHAR

2. 2. VARCHAR / VARCHAR2

3. 3. DATE

4. 4. NUMBER

5. 5. LARGE OBJECTS

i. i. Character Large Object .

ii. ii. Binary Large Object .

NOTE : SQL is not a Case Sensitive Language .

1. CHAR : In character datatype we can store 'A-Z' , 'a-z' , '0-9'

And Special Characters( $ , & , @ , ! … ) .

Characters must always be enclosed within single quotes ' '.
Whenever we use char datatype we must mention size
Size : it is used to specify number of characters it can store .

The maximum number of characters it can store is 2000ch.

Char follows fixed length memory allocation .

Syntax: CHAR ( SIZE )

2.VARCHAR : In varchar datatype we can store 'A-Z' , 'a-z' , '0-9'

And Special Characters( $ , & , @ , ! … ) .

Characters must always be enclosed within single quotes ' '.
Whenever we use char datatype we must mention size
Size : it is used to specify number of characters it can store .

The maximum number of characters it can store is 2000ch.

VarChar follows variable length memory allocation .

Syntax: VARCHAR ( SIZE )

Example : VARCHAR ( 8 )

NOTE : VARCHAR2 : it is an updated version of varchar where in We can store up to 4000Ch.

Syntax: VARCHAR2( SIZE )

3. NUMBER : It is used to store numeric values .

SYNTAX: NUMBER ( Precision , [ Scale ] )

[ ] - Not Mandatory .

Precision : it is used to determine the number of digits used To store integer value .

Scale : it is used to determine the number of digits used to store Decimal ( floating ) value within the precision .

➢ Scale is not mandatory , and the default value of scale Is zero ( 0 ) .

4. DATE : it is used to store dates in a particular format . It used Oracle specified Format.

Example:

DOB	Hire date	Anniversary

Date	Date	Date

'01-JAN-1945’ ‘20-JUN-20' '15-APR-2008'

5. LARGE OBJECTS

1. Character large object (CLOB):

It is used to store characters up to 4 GB of size.

2.Binary large object (BLOB):

It is used to store binary values of images, mp3, mp4 Documents etc. …. Up to 4GB of size.

CONSTRAINTS:

It is a rule given to a column for validation.

Types of Constraints:

1. UNIQUE

2. NOT NULL

3. CHECK

4. PRIMARY KEY

5. FOREIGN KEY.

1. UNIQUE: "It is used to avoid duplicate values into the column ".

2. NOT NULL: "It is used to avoid Null ".

3. CHECK: "It is an extra validation with a condition

If the condition is satisfied, then the value is accepted else Rejected ".

4. PRIMARY KEY: "It is a constraint which is used to identify a record Uniquely from the table "

Characteristics of Primary key:

➢ We can have only 1 PK in a table

➢ PK cannot accept duplicate / repeated values.

➢ PK cannot accept Null

➢ PK is always a combination of Unique and Not Null Constraint.

5. FOREIGN KEY: "It is used to establish a connection between the the tables "

Characteristics of Foreign key:

➢ We can have only Multiple FK in a table

➢ FK can accept duplicate / repeated values.

➢ FK can accept Null

➢ FK is not a combination of Unique and Not Null Constraint.

➢ For an Attribute (column) to become a FK, it is mandatory That it must be a PK in its own table .

Example:

Primary key Check ( Salary > Check

Differentiate between Primary key and Foreign key .

	PRIMARY KEY			FOREIGN KEY

	It is used to identify a records			It is used to establish a connection
	Uniquely from the table.			Between the tables

	It cannot accept Null			It can accept Null

	It cannot accept duplicate values			It can accept duplicate values

	It is always a combination of			It is not a combination of
	Not Null and Unique constraint			Not Null and Unique constraint

	We can have only 1 PK in a table			We can have Multiple FK in a table

NOTE : NULL

Null Is a keyword which is used to represent Nothing / Empty Cell.

Characteristics of Null :

➢ Null doesn’t represent 0 or Space .

➢ Any operations performed on a Null will result in Null itself

➢ Null doesn’t Occupy any Memory .

➢ We cannot Equate Null .

OVERVIEW OF SQL STATEMENTS :

1. DATA DEFINITION LANGUAGE ( DDL )

2. DATA MANIPULATION LANGUAGE ( DML )

3. TRANSCATION CONTROL LANGUAGE ( TCL )

4. DATA CONTROL LANGUAGE ( DCL )

5. DATA QUERY LANGUAGE ( DQL )

DATA QUERY LANGUAGE ( DQL ) :

"DQL is used to retrieve the data from the database " . It had 4 statements :

1. SELECT

2. PROJECTION

3. SELECTION

4. JOIN

1. SELECT : "It is used to retrieve the data from the table and display it.

2. PROJECTION : "It is a process of retrieving the data by selecting only the columns is known as Projection "

➢ In projection all the records / values present in a particular column are by default selected .

3.SELECTION : "It is a process of retrieving the data by selecting both the columns and rows is known as Selection " .

4.JOIN :"It is a process of retrieving the data from Multiple tables simultaneously is known as Join " .

PROJECTION

➢ "It is a process of retrieving the data by selecting only the columns is known as Projection " .

➢ In projection all the records / values present in a particular column are by default selected .

SYNTAX :

SELECT * / [DISTINCT] Column_Name / Expression [ALIAS] FROM Table_Name ;

ORDER OF EXECUTION

1. FROM Clause

2. SELECT Clause

Example : Write a query to display names of all the students .

NOTE :

➢ FROM Clause starts the execution .

➢ For FROM Clause we can pass Table_Name as an argument .

➢ The job of FROM Clause is to go to the Database and search for the table and put the table under execution .

➢ SELECT Clause will execute after the execution of FROM Clause

➢ For SELECT Clause we pass 3 arguments

*
Column_Name
Expression

➢ The job of SELECT Clause is to go the table under execution and select the columns mentioned .

➢ SELECT Clause is responsible for preparing the result table .

➢ Asterisk(*) : it means to select all the columns from the table .

➢ Semicolon : it means end of the query .

➢ WAQTD student id and student names for all the students.

SELECT SID , SNAME FROM STUDENT ;

➢ WAQTD name and branch of all the students .

SELECT SNAME , BRANCH FROM STUDENT ;

➢ WAQTD NAME , BRANCH AND PERCENTAGE FOR ALL THE STUDENTS .

SELECT SNAME , BRANCH , PER FROM STUDENT ;

➢ WAQTD details of all the students from students table .

SELECT *

FROM STUDENT ;

➢ WAQTD sname , sid , per , branch of all the students .

SELECT SNAME , SID , PER , BRANCH FROM STUDENT ;

EMP Table :

WAQTD name salary and commission given to all the employees .

Select ename , sal , comm From emp ;

➢ WAQTD name of the employee along with their date of joining .

Select ename , hiredate From emp ;

➢ WAQTD dname and location for all the depts .

Select dname , loc From dept ;

QUESTIONS ON EMP AND DEPT TABLE:

1.WRITE A QUERY TO DISPLAY ALL THE DETAILS FROM THE EMPLOYEE TABLE.

2.WAQTD NAMES OF ALL THE EMPLOYEES.

3.WAQTD NAME AND SALARY GIVEN TO ALL THE EMPLOYEES.

4.WAQTD NAME AND COMMISSION GIVEN TO ALL THE EMPLOYEES.

5.WAQTD EMPLOYEE ID AND DEPARTMENT NUMBER OF ALL THE EMPLOYEES

IN EMP TABLE.

6.WAQTD ENAME AND HIREDATE OF ALL THE EMPLOYEES .

7.WAQTD NAME AND DESIGNATION OF ALL THE EMPLPOYEES .

8.WAQTD NAME , JOB AND SALARY GIVEN ALL THE EMPLOYEES.

9.WAQTD DNAMES PRESENT IN DEPARTMENT TABLE.

10.WAQTD DNAME AND LOCATION PRESENT IN DEPT TABLE.

DISTINCT Clause

"It is used to remove the duplicate or repeated values from the Result table " .

Distinct clause has to be used As the first argument to select clause .
We can use multiple columns As an argument to distinct clause, it will remove the combination of columns in which the records are duplicated .

Example:

SELECT SNAME FROM STUDENT;

➢ SELECT DISTINCT SNAME FROM STUDENT ;

➢ SELECT DISTINCT BRANCH FROM STUDENT ;

➢ SELECT DISTINCT PER FROM STUDENT ;

➢ SELECT DISTINCT BRANCH , PER FROM STUDENT;

OVERVIEW OF SQL STATEMENTS :

1. DATA DEFINITION LANGUAGE ( DDL )

2. DATA MANIPULATION LANGUAGE ( DML )

3. TRANSCATION CONTROL LANGUAGE ( TCL )

4. DATA CONTROL LANGUAGE ( DCL )

5. DATA QUERY LANGUAGE ( DQL )

DATA QUERY LANGUAGE ( DQL _) :

"DQL is used to retrieve the data from the database " .

It had 4 statements :

1. SELECT

2. PROJECTION

3. SELECTION

4. JOIN

1. SELECT : "It is used to retrieve the data from the table and display it.

2. PROJECTION : "It is a process of retrieving the data by selecting only the columns is known as Projection " .

➢ In projection all the records / values present in a particular column are by default selected .

3. SELECTION : "It is a process of retrieving the data by selecting both the columns and rows is known as Selection " .

4. JOIN :"It is a process of retrieving the data from Multiple tables simultaneously is known as Join " .

PROJECTION

➢ "It is a process of retrieving the data by selecting only the columns is known as Projection " .

➢ In projection all the records / values present in a particular column are by default selected .

SYNTAX :

SELECT * / [DISTINCT] Column_Name / Expression [ALIAS] FROM Table_Name ;

ORDER OF EXECUTION

1. FROM Clause

2. SELECT Clause

Example : Write a query to display names of all the students .

DAY 6

EXPRESSION

"A statement which gives result is known as Expression ".

Expression is a combination Operand and Operator .

Operand : These are the values that we pass .

Operator : These are the Symbols which perform some Operation on the operand

Example: 5*10

1. WAQTD name and salary given to the employees .

SELECT ENAME , SAL FROM EMP ;

2. WAQTD name and annual salary of the employees . SELECT ENAME , SAL * 12

3. FROM EMP ;

4. WAQTD all the details of the employee along with annual salary

Select eid , ename , sal , sal*12 From emp ;

Select emp.* , sal*12 From emp ;

5. WAQTD name and salary with a hike of 20% .

Select ename , Sal + Sal*20/100 From emp ;

Formulae to calculate percentage :

6. WAQTD name and salary of an employee with a deduction Of 10% .

Select ename , sal - sal * 10 /100 From emp ;

ALIAS

"It is an alternate name given to a Column or an Expression In the result table " .

○ We can assign alias name with or without using 'As' keyword .

○ Alias names have to be a single string which is separated by An underscore or enclosed within double quotes

WAQTD annual salary for all the employees .

Select sal*12 From emp ;

Advanced Python Interview questions

2022-02-14T22:39:00.003-08:00

Advanced Python Interview questions:

1) What is the difference between method and constructor ?

Method
1) Name of method can be any name
2) Method will be executed if we call that method
3) Per object, method can be called any number of times.
4) Inside method we can write business logic

Construtor
1) __new__ and __init__ collectively form constructor.
2) Object initialization is controlled by an instance method called __init__ and which is also usually called as Constructor. Once the object is created,we can make sure that every variable in the object is properly initialized by defining an __init__ method in our class, which means init-iate
3) Constructor will be executed automatically at the time of object creation.
4) Per object, Constructor will be executed only once
5) Inside Constructor we have to declare and initialize instance variables

2) Explain different types of methods in Python?
Python has three types of methods:

1) Instance Methods

2) Class Methods

3) Static Methods

1)Instance Methods:

This is called if the class has been instantiated.
Instance method has to be declared with self variable.Example - def test(self):
By using self variable,method can o access instance variables.
Within the class we can call instance method by using self variable and from outside of the class we can call by using object reference.

class Student:

def __init__(self,name)

self.name=name

def display(self)

print('My name is ',self.name)

2) Class Methods

This method does not require self as argument and they use only class variable.
They need a parameter called cls. This stands for class and like self it gets automatically passed by python
This methods needs to be declared using @classmethod decorator.
We can call this method using classname or object reference variable

class Bird:

legs = 2

@classmethod

def walk(cls,name):

print('{} walks with {} legs...'.format(name,cls.lEgs))

Bird.walk('Crow')

3) Static Methods

These methods are general utility methods.
These methods do not use any instance or class variables.
This method does not require self or cls arguments at the time of declaration.
This can be declared exlicitly by using @staticmethod decorator
We can access static methods by using classname or object reference

class Mathfunc:
@staticmethod
def add(x,y)
print('The Sum:',x+y)

Mathfunc.add(10,20)

3) Can tuple be used as dictionary keys?
Yes.
Only immutable elements can be used as dictionary keys.Hence only tuples and not lists can be used as keys.
d={}

t1 = (5,9)
t2 = (30,40,9)

d[t1] = 7
d[t2] = 90

print d[t1], d[t2]

Output:

7 90

4)Which OOP’s concept is not applicable in Python?

Python Method overloading is not possible.
If we are trying to declare multiple methods with same name and different number of arguments then Python will always consider only last method.

5)How to handle Overloaded Method Condition in Python?

Most of the times, if method with variable number of arguments required then we can handle with default arguments or with variable number of argument methods.

Default Arguments:
class Test:
def sum(self,a=None,b=None,c=None):
if a!=None and b!= None and c!= None:
print('The Sum of 3 Numbers:',a+b+c)
Variable Number of Arguments:
class Test:
def sum(self,*a):
for x in a:
print(x)

6) What is the difference between yield and return statement?

Return	Yield
‘return’ statement causes the function to exit and arrives back the value to caller, then function loses its local state. Thus calling it next time it starts from first statement	‘yield’ statement cause the function to return back a generator object to the caller and maintains states between func calls .Thus resumes from where it left off when we call next() method again
It is used when function is ready to exit and return a value back to the caller	It is used to calculate series of results 1 by 1 on the fly
It will exit the function	It will not cause function to exit
It will terminate the loop immediately	Does not terminate the loop
Returns single value to the caller function	It returns generator object which can parse into list

7)Difference between str() and repr()

Difference between __str__() and __repr__()

str() internally calls __str__() function and hence functionality of both is same.
repr() internally calls __repr__() function and hence functionality of both is same.

str()

str() returns a string containing a nicely printable representation object.
The main purpose of str() is for readability.It may not possible to convert result string to original object to original object

import datetime

today=datetime.datetime.now()

s=str(today)#converting datetime object to str

print(s)

d=eval(s)#converting str object to datetime

Output

2020-06-13 16:57:36.425246

Traceback (most recent call last):

File "<string>", line 1

2020-06-13 16:57:36.425246

SyntaxError: Invalid token

repr()

repr() returns a string containing a printable representation of object.
The main goal of repr() is definite. We can convert result string to original object by using eval() function,which is possible in str() function.

import datetime

today=datetime.datetime.now()

s=repr(today)#converting datetime object to str

print(s)

d=eval(s)#converting str object to datetime

Output : datetime.datetime(2020, 6, 13, 16, 59, 18, 355503)

8) How to remove directory/directories in python?

Python provides inbuilt module os,which contains several functions to perform directory related operations.

import os

os.rmdir("mysub/mysub2") #Remove single dir
print("mysub2 directory deleted")

os.removedirs("sub1/sub2/sub3") # Remove multiple dirs

print("All 3 directories sub1,sub2 and sub3 removed")

9) Explain Garbage collection in Python?

Main objective of Garbage Collector is to destroy useless/unusable objects
Garbage collection is the process of cleaning computer memory which is currently being put to use by a running program when that program no longer needs that memory
With Garbage collection, that chunk of memory is cleaned so that other programs (or same program) can use it again.

Automatic garbage collection of cycles
Python handles its objects by keeping a count to the references each object have in the program, i.e each object stores how many times it is referenced in the program. This count is updated with the program runtime and when it reaches zero, this means it is not reachable from the program anymore. Hence, the memory for this object can be reclaimed and be freed by the interpreter.

Manual garbage collection
The garbage collector can be called manually in the following way:
import gc
collected = gc.collect()
print "Garbage collector: collected %d objects." % (collected)
gc.collect() returns the number of objects it has collected and deallocated. You can print this information in the following way:

By default Garbage collector is enabled, but we can disable based on our requirement. In this context we can use the following functions of gc module.
1) gc.isenabled() Returns True if GC enabled
2) gc.disable() To disable GC explicitly
3) gc.enable() To enable GC explicitly

10) What is function decorator?

Decorators are used to wrap/cover a function within another function. It takes a function as argument and extend its functionality and return modified function with extended feature
The main objective of decorator is to extend the functionality of existing function without modifying it

def wish(name):

print("Hello",name,"Good Morning")

This function can always print same output for any name

But we need modify this function to provide different message if name is “Seetha”,We can do this without modifying wish() function by using decorator.

def decor(func):

def inner(name):

if name=="Seetha":

print("Hello Seetha Good Day!!")

else:

func(name)

return inner

@decor

def wish(name):
print("Hello",name,"Good Morning")

wish("Tina")

wish(“Seetha")

Output: Hello Tina Good Morning

Hello Seetha Good Day!!

In the above program whenever we call wish() function automatically decor function will be executed.

11)What is lambda function ?

A function without any name. Nameless functions are called anonymous functions or lambda functions.
The main purpose of anonymous function is just for instant use or one time usage
It is a function-like callable that is not defined with a def statement.
Python lambdas are only a shorthand notation if you are too lazy to define a function.

Syntax of lambda Function:
lambda argument_list : expression

Normal Function:
We can define by using def keyword.
def squareIT(n):
return n*n

lambda Function:
We can define by using lambda keyword
lambda n:n*n

Advantages:

By using Lambda Functions we can write concise code so that readability of the program will be improved.
Lambda Function internally returns expression value and do not required to have return statement explicitly.
Sometimes we can pass function as argument to another function. In such cases lambda functions are best choice.
We can use lambda functions very commonly with filter(),map() and reduce() functions as these functions expect function as argument.

12) What are generator function ?

Generator is a function which contains yield statement/keyword
The difference between normal function and generator function is instead of returning one value with return statement, we can yield several values one at a time.
Based on yield statement, it allows to pause/freeze a function and return an immediate result. Generator function saves its execution context and so can be resumed later.
When generator function is called, the code in the function body is not executed but an iterator is returned
Return statement in the generator should stop the execution. Return can be called without arguments when it is used inside generator

Generators contains of two components:

generator-function
generator-iterator

Generator function is statements defined within function definition with yield statement
Generator iterator is what the function returns.Generally these two entities are treated as one and its called a generator

Example:
>>> def test_generator():
yield 1
...
>>> test_generator
<function test_generator at 19bb>

>>>test_generator()
<generator object at 163b>

13)Explain how to build command-line options in Python? OR How to read the values from the terminal?

The ‘argparse’ module is a command line interface. We will use ‘argparse’ module to read the values from the Terminal.
The program defines what arguments it requires, and argparse will figure out how to parse those out of sys.argv.

Using the Python argparse library has four steps:
1) Import the Python argparse library
2) Create the parser
3) Add optional and positional arguments to the parser
4) Execute .parse_args()

Example:
import argparse
my_parser = argparse.ArgumentParser()
my_parser.add_argument('--input', action='store', type=int, required=True)
my_parser.add_argument('--id', action='store', type=int)

args = my_parser.parse_args()
print(args.input)

$ python test.py --in 42
42

Uses of the Python argparse Library
1) Setting the Name of the Program
2) Displaying a Custom Program Usage Help
3) Displaying Text Before and After the Arguments Help
4) Customizing the Allowed Prefix Chars
5) Setting Prefix Chars for Files That Contain Arguments to Be Included
6) Allowing or Disallowing Abbreviations
7) Using Auto Help

14)What are pros and cons of using generators?
Pros:

Saves Memory space - Iterators do not calculate the value of each item when instantiated. They compute it when its asked for. This is called lazy evaluation.Lazy evaluation is beneficial when we have large data set to compute. It allows us to use data immediately while the whole data set is being calculated.
Generators easy to implement as they inevitably implement next(), iter() & StopIteration or else had to be explicitly implemented.
Improves performance and are best suitable for reading data from large set of large files
Generators work best for web scraping and crawling

Cons:

Generators can only be iterated over once. If we try to iterate over it again, no value will be returned. It will behave like an empty list.

15) Explain constructor overloading in Python?

Constructor overloading is not possible in Python.
If we define multiple constructors then the last constructor will be considered

class Test:

def __init__(self):

print('No-Arg Constructor')

def __init__(self,a):

print('One-Arg constructor')

t1=Test()

Output: Error

16) How to fetch shell environment variables in python?
>>> import os
>>> os.environ.keys( )
['WINBOOTDIR', 'PATH', 'USER', 'PP2HOME', 'CMDLINE', 'PYTHONPATH', 'TEMP', 'PROMPT', 'WINDIR', 'TMP']

17)What are abstract method?

Methods with only declaration and without implementation is called abstract method.
We can declare abstract method by using @abstractmethod decorator
@abstractmethod decorator is present in abc module. Hence it is required to import abc module, else it will throw an error.

class Sample:
@abstractmethod
def test(self):
pass
NameError: name 'abstractmethod' is not defined

from abc import *
class Sample:
@abstractmethod
def test(self):
pass

18)Can we have Public, Protected and Private Attributes in Python?
Public:
In Python by default all attributes/members are Public. Hence it can be accessed anywhere within the class or from outside the class.
Ex : name = “Srishti”

class employee:
def __init__(self, name, sala):
self.name=name
self.sala =sala

>>> e1=employee("Srishti",10000)
>>> e1.salary
10000
>>> e1.salary=20000
>>> e1.salary
20000

Protected:

Protected attributes/members of a class can be accessed within the class and available to its child classes only . No other environment is allowed to access it
We can specify an protected attribute in python by pre-fixing with _ (single underscore) symbol.

Syntax: _variablename = value
Eg: _name='Vanahalli'

class employee:
def __init__(self, name, sala):
self._name=name # protected attribute
self._salary=sala # protected attribute

But it is just convention and in in reality protected attributes does not exist. Below operation is still possible
>>> e1=employee("Vanahalli", 10000)
>>> e1._salary
10000
>>> e1._salary=20000
>>> e1._salary
20000

Private:

Private attributes/members can be accessed within the class only. It is not accessible from outside the class or child classes
Private variables can be declared by explicitly pre-fixing double underscored __ . Any attempt to access it will result in AttributeError

syntax: __variablename=value

class employee:
def __init__(self, name, sala):
self.__name=name # private attribute
self.__salary=sala # private attribute

>>> e1=employee("Bill",10000)
>>> e1.__salary
AttributeError: 'employee' object has no attribute '__salary'

19)How to Access Private Variables from Outside of the Class ?

Python internally performs name twisting of private variables/attributes.
Every attribute with double underscore will be changed to object._classname__variable
Hence if we need to access private variables outside the class, we can do it as below. But this is not recommended.

class Sample:

def __init__(self):

self.__x=20

x=Sample()

print(x._Sample__x)#20

20) What is the difference between del and None?
del

del is used to delete object and removes the binding of the variable
Since the variable will be removed, we cant access the variable ( un bind operation)

a= “test”
del a
Print(a) -> NameError: name a is not defined
None

In the case of None assignment, the variable will not be removed but the corresponding object is eligible for garbage collection ( re-bind operation).
Hence after assigning None value to the variable, we can still access it

a="test"
a=None
print(a) # None

21) Can tuples be modified?
Python tuple has amazing feature: they are immutable, but their values may change.
This may happen when a tuple holds a reference to any mutable object, such as a list.

>>> t=(1,[1,2,3])
>>> t[1][2]=5
>>> t
(1, [1, 2, 5])
>>>

22)What is pass statement ?

pass is a keyword in Python.
To define an empty block we use pass keyword . It defined empty block with pass keyword
It is basically an empty/null statement and doesn’t do anything

Example:
if True:
SyntaxError: unexpected EOF while parsing

if True: pass

def test():
SyntaxError: unexpected EOF while parsing

def test(): pass

use case of pass:
If we need parent class to contain a function with no implementation and expect child class method be responsible for code implementation, we can define parent class method using pass statement

23) What is super method in python?

super() is a built-in method which is used to call the super class constructors,variables and methods from the child class.
class Person1:
def __init__(self,name):
self.name=name

def display(self):
print('Name is :',self.name)

class Student1(Person1):
def __init__(self,name,rollno):
super().__init__(name)
self.rollno=rollno

def display(self):
super().display()
print('Roll No:',self.rollno)

t1=Student1('Srishti',101)
t1.display()

Output:
Name is: Srishti
Roll No: 101

24) Explain about the special variable __name__?

Every python program will be added with a special variable __name__
This variable stores information about the program is executed as an individual program or as a module.
If the program is executed as individual program then this variable value will be __main__
If the program executed as a module from some other program then the value of this variable will be name of module where it is defined.
Hence by using this __name__ variable we can identify whether the program executed directly or as module.

module1.py:
def func():
if __name__=='__main__':
print("The code executed as main pgm")
else:
print("The code executed as a module “)

func()

test.py:
import module1
module1.func()

C:\Python>python module1.py
The code executed as main pgm

D:\Python>python test.py
The code executed as a module

25) What is shallow copy?

Shallow copy of any python object makes a copy of the object itself . It also creates reference to the objects contained in the list
Shallow copy can be achieved by slice operator

>>>Vowel = [‘a’,’e’,’I’,’o’,’u’]
>>>V_copy = Vowel[:]
>>> Vowel is V_copy
0
>>>Vowel == V_copy
1
We can use copy(object) func of the copy module
>>import copy
>>high = copy.copy(Vowel)
>>> high is Vowel, high == Vowel
(0,1)

26) what is use of setdefault() method?

The setdefault() method allows to set a value in dictionary for certain key if that key does not previously have a value
It takes key to check for as the first element and value to set at the key as second.
If key does exits, then this method method returns key’s value.

msg = ' Srishti'
cnt = {}
for c in msg:
cnt.setdefault(c, 0)
cnt[c] = cnt[c] + 1
print(cnt)

Output
C:/TEST_PGMS> python test.py

{' ': 1, 'S': 1, 'r': 1, 'i': 2, 's': 1, 'h': 1, 't': 1}

The program loops over each character in the msg,counting how often each character seems.
The setdefault() method call ensures that the key is in the cnt dictionary (with a default value of 0) so the program doesn’t toss a KeyError error when cnt[c] = cnt[c] + 1 is performed.

27) What are different types of function arguments in Python?

In a function func1 – x,y are called formal arguments and 1,2 are called actual arguments
def func1 (x , y): pass
func1(1,2)

There are 4 types are actual arguments are allowed in Python.
1. Positional argument
2. Keyword argument
3. Default argument
4. Variable length argument

1. Positional arguments:

These are the arguments need to be passed to function in precise positional order.
The number of arguments and position of arguments must match. If we change the order the result would be changed. If number of arguments differ, it will result in Error
Positional-only parameters are placed before a / (forward-slash). The / is used to logically distinct the positional-only parameters from the rest of the parameters

def pos_only_arg(arg, /):
print(arg)

def sub(x,y):
print(x-b)

sub(20,40)
sub(40,20)

2. Keyword arguments/ named arguments

We can pass argument values by keyword and a = sign
Keyword is the key or parameter name and value is the value or object to be passed as that keyword
The order of the arguments does not matter but number of arguments must be matched
To notify parameters as keyword-only, representing parameters must be passed by keyword argument, place an * in the arguments list just before the first keyword-only parameter.

def kwd_only_arg(*, arg):
print(arg)

def hello(name,msg):
print("Hello",name,msg)
hello(name="Satish",msg="Good Morning")

Output
Hello Satish Good Morning

Note: In a function call, we can have positional and keyword arguments together specified. Always Positional arguments must be at the beginning followed by keyword arguments if not we get Syntax error

def test(volume, number='hello', action='sum’, type='Red'): pass

Valid:
test(volume=10) # 1 keyword argument
test(volume =100, action='done') # 2 keyword arguments
test(action='done’, volume =100) # 2 keyword arguments
test('this', 'is', 'positional') # 3 positional arguments
test('hundred', number='I am number') # 1 positional, 1 keyword

Invalid
test(actor='Deepika') # unknown keyword argument
test() # required argument missing
test(volume=2.0, '200') # non-keyword argument after a keyword argument
test(110, volume=220) # duplicate value for the same argument

3. Default argument

Default arguments are those positional arguments that take default values if no explicit values are passed to these arguments from the function call.
Let's define a function with one default argument.

def find_one(int1=2, int2=3):
result = int1 * int2
return result

4. Variable length arguments

We can create functions to accept any number of arguments. These functions can accept an unknown amount of input, also as successive entries or named arguments.
we can use the *args or **kwargs syntax to capture a variable number of arguments in functions. By adding * and ** (one or two asterisks) to the beginning of parameter name in the function definition we can specify an arbitrary/varibale number of arguments

def test_varargs(*args, **kwargs):
print(args)
print(kwargs)

*args: Receive multiple arguments as a tuple
**kwargs: Receive multiple keyword arguments as a dictionary

NOTE
When mingling the positional and named arguments, positional arguments should come before named arguments. Additionally, arguments of a fixed length come before arguments with variable length. So, we can order like below:
1) Known positional arguments
2) *args
3) Known named arguments
4) **kwargs

A function with all types of arguments will be like
def all_in_one_function (number1, number2, *args, callmeback=None, msgs=[], **kwargs):
pass

28) How to detect the scope of a Variable ?

Python has two built-in methods called globals() and locals().
They let us determine whether a variable is either part of the global namespace or local namespace.
The following example shows how to use these methods:

def test():
global address
address = "bangalore"
name = "Satish"

print("Address in global:", 'Address' is globals())
print("Address in local :", ' Address ' in locals())
print("name in global :", 'name' in globals())
print("name in local :", 'name' in locals())
return

address = "Gadag"
print (address)
test()

The output is as below and display the scope of the two variables address and name inside the function test():

$ python test.py
Gadag
Address in global: True
Address in local : False
name in global : False
name in local : True

29) Explain different types of variables in python?
A variable is an concept for the memory cells that contain the actual value. It is easy to remember the name of the memory cell than to recall its physical memory address.
All the variables are portion of the some namespace and hence have the some scope.

Unless redefined as a local variable well along a variable defined in the main program belongs to the global namespace, that can be accessed by any function in the Python program

Python supports 2 types of variables.
1. Global Variables
2. Local Variables
3. Nonlocal variable(only from Python3)

1. Global Variables

The variables which are declared outside of function are called global variables.
These variables can be accessed in all functions of that module.
A variable cannot be be both local and global inside any function.
Python will decide that we want a local variable due to the assignment to s inside test(), so the first print statement before the definition of s throws the error message. Any variable which is altered or created inside a function is local, if it is not been declared as a global variable.
To express Python that we want to use the global variable, we have to clearly tell this by using the keyword "global", as seen in the following example:

Example1:
def test():
global s
print(s)
s = "Only in winter Bangalore weather is Good"
print(s)

s = "I am looking for python course"
test()
print(s)

Output:
I am looking for python course
Only in winter Bangalore weather is Good
Only in winter Bangalore weather is Good

Example2:
a=100 # global variable
def func1():
print(a)

def func2():
print(a)

func1()
func2()

Output
100
100

NOTE:We can use global keyword for the following purposes:
1. To declare global variable inside function
2. To make global variable available to the function so that we can perform required alterations

2. Local Variables:

The variables which are declared inside a function are called local variables.
Local variables are available only for the function in which we its declared i.e from outside of function we cannot access.

def fun1():
a=10
print(a) # valid

def fun2():
print(a) #invalid

fun1()
fun2()

NameError: name 'a' is not defined

3) Nonlocal Variables

Nonlocal variables are used in nested functions whose local scope is not defined. This means that the variable can be neither in the local nor the global scope.
One difference to global variables is that its not possible to change variables from the module scope, i.e. variables which are not defined inside of a function by using the nonlocal statement.
We use nonlocal keyword to create nonlocal variables.

def out():
x = "out_func"

def in():
nonlocal x
x = "nonlocal_var"
print("in:", x)

in()
print("out:", x)

out()

Output:
In:nonlocal_var
out:out_func

30)Why is python string immutable

Improved performance. String is immutable hence we can allocate space for it during creation time and the storage necessities are fixed and remains unchanged.
Strings in Python are measured as “fundamental” as numbers

31)Difference between is and ==

• An is expression evaluates to True if two variables point to the same (identical) object.

• An == expression evaluates to True if the objects referred to by the variables are equal (have the same contents).

Example1:

>>> a = (1,2,3)

>>> b=(1,2,3)

>>> a == b

True

>>> a is b

False

>>> id(a), id(b)

(671301, 789098)

Example2:

>>> c=a

>>> c

('1',’2’,’3’)

>>> c == a

True

>>> c is a # because c and a refer to the same object

True

32) Function vs Module vs Library
1. A group of lines with a name is called a function
2. A group of functions saved to a file is called Module
3. A group of Modules is called Library

33)How to run Other Programs from Python Program

Method 1 OS Module contains system() function to run programs and commands.
os.system("commad string").The argument is any command which is executing from DOS.
import os
os.system("dir *.py")
os.system("py test.py")

Method 2:
To run an external command without interacting with it, as we do with os.system() we can use the call() function from subprocess module.
import subprocess
# Simple command
subprocess.call(['ls', '-1'], shell=True)

The command line arguments are passed as a list of strings, which avoids the need for escaping quotes or other special characters that might be interpreted by the shell.

The subprocess module allows you to spawn new processes, connect to their input/output/error pipes, and obtain their return codes. This module intends to replace several older modules and functions:
os.system
os.spawn*

34)Explain about the hashable objects in python?

An object is hashable if it has a hash value which never alters during its lifetime (it needs a __hash__() method) and can be compared to other objects (it needs an __eq__() or __cmp__() method). Hashable objects which compare equal must have the same hash value.
Hashable objects are integers, floats, strings, tuples, and frozensets. Note that all hashable objects are also immutable objects.
Objects which are instances of user-defined classes are hashable by default, they all compare unequal, and their hash value is their id().
The key of a dictionary should be unique. Internally, the key is transformed by a hash function and become an index to a memory where the value is stored. Suppose, if the key is changed, then it will be pointing somewhere else and we lose the original value the the old key was pointing.
Tuples are not always hashable because tuples may hold references to unhashable objects such as lists or dicts. A tuple is only hashable if all of its items are hashable

>>> t1 = (109, 'Z', frozenset([1, 2, 3]))
>>> t2 = (1, 'r', {1, 2, 3})
>>> hash(t1) # OK!
1315572702399614049
>>> hash(t2) # NOT OK!
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: unhashable type: 'set'

Mutable objects are lists, dictionaries, and sets which are not hashable

35) How to identify data type of any object in python?

We can retrieve type of any object by passing the object to type(obj) function.
>>> i=10
>>> type(i)
<class 'int'>
>>> x = (1,2)
>>> type(x)
<class 'tuple'>

36) What is Namedtuple?

Namedtuple is a tuple where each value has a pre-assigned name
Namedtuples are immutable containers similar to regular tuples. Once we save data in top-level attribute on a namedtuple, we cannot alter them by updating the attribute. All attributes on a namedtuple object follow the principle - “write once, read many”
Each object stored in namedtuple can be retrieved through a unique,human-readable identifier and we do not have to remember integer indexes.
A named tuple can be accessed like a class attribute
Named tuples that are available from the collections module can be used to access values with object notation as shown below:

>>> from collections import namedtuple
>>> student = namedtuple('student','name,marks')
>>> s1 = student('satish',150)
>>> s1.name
'satish'
>>> s1.marks
150
>>> type(s1)
<class '__main__.student'>

38)Why must dictionary keys be immutable?

The hash table implementation of dictionaries uses a hash value calculated from the key value to find the key. If the key were a mutable object, its value could alter and thus its hash could also change.
But since whoever changes the key object can’t tell that it was being used as a dictionary key, it can’t move the entry around in the dictionary. Then, when you try to look up the same object in the dictionary it won’t be found because its hash value is different. If you tried to look up the old value it wouldn’t be found either, because the value of the object found in that hash bin would be different.
If you want a dictionary indexed with a list, then convert the list to a tuple first, the function tuple(L) creates a tuple with the same entries as the list L. Tuples are immutable and can therefore be used as dictionary keys.

39) How do you read an entire file?

Python provides numerous methods to read the entire contents of a file.

open the file and call the read() function. This will read the entire contents of the file until an EOF marker is met and returns the contents of the file as a string.
open the file and use the readlines() function. This reads the entire contents of the file, separating each line into individual strings, until an EOF marker is reached. Once the end of the file is found, a list of strings representing each line is returned.
In case of very large files we might want to read only a specific number of bytes at a time.Then use the read(bytes) function to read a specific number of bytes at a time, which can then be processed more easily. This will read a specific number of bytes from the file if possible and return them as a string. If the first character read is an EOF marker, null is returned.

filePath = "input.txt"

#Read entire file into a buffer
buffer = open(filePath, 'rU').read()
print buffer

#Read lines into a buffer
inList = open(filePath, 'rU').readlines()
print inList

#Read bytes
file = open(filePath, 'rU')
bytes = file.read(5)
if bytes:
print bytes

osx-$ python t.py
hi
hello
line
ends
here

['hi\n', 'hello\n', 'line\n', 'ends\n', 'here\n']
hi
he

40) How do you swap keys for Values in a dictionary?

This is useful when we are using dictionary in which we often need to look up items by value. Rather than searching through the entire dictionary each time, we could create an alternate dictionary that has the values swapped.
To swap the keys and values in a dictionary iterate through the items in the dictionary using the iteritems method and use the values as keys assigning the original key as the value.

myDict = {'colour':'red', 'nu':6}
#Swap keys for value
swapDict = {}
for key, val in myDic.iteritems():
swapDict[val] = key

print swapDic

OUTPUT:

{'red': 'colour', 6: 'nu'}

41) How do you list directory tree or walking the directory tree in python?

The walk(path) function will walk the directory tree, and for each directory in the tree create a three-tuple containing (1) the dirpath, (2) a list of dirnames, and (3) a list of filenames.
Every tuple contains

Index 0 - path to the directory
Index 1 - Lists of the subdirectories
Index 2 - files contained in the directory

import os

tree = os.walk('/Users/qauser')

for directory in tree:

print(directory)

Output

('/tmp/test', [], ['file2', 'fil1'])

42) Explain zip() to process iterators in parallel ?

Zip aggregates two or more iterators with a lazy generator. The zip generator yields tuples containing the next value from each iterator. It takes iterables (can be zero or more) wrap them in a tuple and return it
It keeps yielding tuples until a wrapped iterator is exhausted. . This method works if the iterators are of the same length
zip truncates its output silently if you supply it with iterators of different lengths.
Note: The zip_longest function from the itertools built-in module let us iterate over multiple iterators in parallel regardless of their lengths

Return Value from zip()

If we do not pass any parameter, zip() returns an empty iterator
If a single iterable is passed, zip() returns an iterator of tuples with each tuple having only one element.
If multiple iterables are passed, zip() returns an iterator of tuples with each tuple having elements from all the iterables.
Suppose, two iterables are passed to zip(); one iterable containing four and other containing six elements. Then, the returned iterator will contain four tuples. It is because iterator stops when the shortest iterable is exhausted.

n_list = [5, 6, 7]
s_list = ['five', 'six', 'seven']

# No iterables are passed
result = zip()

# Converting itertor to list
r_list = list(result)
print(r_list)

# Two iterables are passed
result = zip(n_list, s_list)
print(result)

# Converting itertor to set
result_set = set(result)
print(result_set)

Output:
[]
[(5, 'five'), (6, 'six'), (7, 'seven')]
set([(6, 'six'), (5, 'five'), (7, 'seven')])

43)How to pass command line arguments in python?

Python standard library called sys and we use an attribute/variable within the module called argv.
The sys.argv variable is a list containing the command-line parameters passed to the program on startup
The first item in the sys.argv list will always be a string holding the program’s filename ('test.py'), and the second item will be the first command line argument

import sys
if __name__ == "__main__":
print(sys.argv)

Output:
$ python a.py test this
['a.py', 'test', 'this']

44) How do you find the number of lines in a file?

When parsing files using Python, it's useful to know exactly how many lines are contained in the file.
It is done by using readlines() to generate a list of lines and using the len() function to determine the number of lines in the list

filePath = "input.txt"
cnt = len(open(filePath, 'rU').readlines())
print "File %s has %d lines." % (filePath,cnt)

Output:
File input.txt has 4 lines.

45)How to raise your own errors?

We have to define and raise exceptions explicitly to indicate that error ,such type of exceptions are called User Defined Exceptions or Customized Exceptions
You can manually throw (raise) an exception in Python with the keyword raise. This is usually done for the purpose of error-checking.
Programmer is responsible to define these exceptions . Hence we need to raise explicitly based on the requirement by using "raise" keyword.
An exception can be a string, a class or an object
Note:
raise keyword is best suitable for customized exceptions but not for pre defined
exceptions

if line_count < 1:
raise error

46) Explain generator function with an example?

A generator object is a Python iterator, so we can use it in for loop

Example:
def test_gen():
z = 0
while z < 2:
yield z
z += 1

>>>num = test_gen()
>>> type(num)
<class 'generator'>
>> for n in num:
... print(num)
0
1
You can also step through one by one, using the built-in next() function:
>>> more_num = test_gen()
>>> next(more_num)
0
>>> next(more_num)
1

>>> next(more_num)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
StopIteration

StopIteration is built-in exception type. It inevitably raised once the generator stops yielding.
It is a signal to for loop to stop looping. Instead we can pass a default value as the second argument to next():

>>> next(more_num, 40)
40

47)How to create dictionaries from lists

k = ['Toy', 'Game', 'Tiger']
v = ['Toys', 'Games', 'Tigers']
#create dict
dc = dict(zip(k, v))
print(dc)
# {'Game': 'Games', 'Tiger': 'Tigers', 'Toy': 'Toys'}
d = dict(enumerate(v))
print(d)
# {0: 'Toys', 1: 'Games', 2: 'Tigers'}

48) Explain Python's documentation tool?

Sphinx is the most widespread Python documentation tool.
It converts the reStructured Text markup language into a range of output formats, including HTML, LaTeX (for printable PDF versions), manual pages, and plain text.
It can be configured with commit hooks to the source repository so that rebuilding of the documentation will happen automatically
reStructured Text Sphinx uses reStructured Text and all Python documentation is written using it. If the content of the long_description argument to setuptools.setup() is written in reStructured Text, it will be condensed as HTML on PyPI—other formats will just be presented as text.
Docstrings placed at the beginning of a module or at the top of an __init__.py file will also appear in help(). Sphinx’s autodoc feature can also automatically generate docu‐ mentation using appropriately formatted docstrings.

Docstring and Block Comments
# This is programmer note
def root(x):
"""Return the square root"""
…..
1) The leading comment block is a programmer’s note.
2) The docstring describes the operation of the function or class and will be shown in an interactive Python session when the when the user types help(root).

49) What is Base case in recursive function?

A base case is a case, where the problem can be solved without further recursion. A recursion can end up in an infinite loop, if the base case is not met in the calls.
The base case returns a value without making any subsequent recursive calls. It does this for one or more special input values for which the function can be evaluated without recursion. For factorial(), the base case is n = 1.

50) How to count occurrences of a character in a Python string?

1. str.count() function

A simple and efficient solution is to get the number of occurrences of a character in string is using the str.count() method. This is best solution to count a single character in a string.

if __name__ == '__main__':

s = "ABADACB"

n = s.count('A')

print(n) # 3

2. collections.Counter class

If you need to find frequency of several characters, calling str.count() method for each character is not recommended. Instead, you should use collections. Counter Python class. It works by storing each character as dictionary keys and their counts as dictionary values.

import collections

if __name__ == '__main__':

s = "ABADACB"

counter = collections.Counter(s)

n = counter['A']

print(n) # 3

The Counter class takes linear time to pre-process the string and offers constant time count operations. However, it occupies some space to store the frequency of each character.

3. Using Dictionary

As an alternate to the collections.Counter class, you can also construct a simple dictionary. The idea is to store each character as dictionary keys and their counts as dictionary values.

if __name__ == '__main__':

s = "ABADACB"

chars = dict.fromkeys(s, 0)

for c in s:

chars[c] += 1

n = chars['A']

print(n) # 3

4. Regular Expressions

You can also use regular expressions to count the number of occurrences of a character in string. However, regular expressions should be best avoided for this trivial task.

import re

if __name__ == '__main__':

s = "ABADACB"

n = len(re.findall('A', s))

print(n) # 3

5. Lambda expressions

Finally, here’s solution using lambda:

if __name__ == '__main__':

s = "ABADACB"

n = sum(map(lambda x: 1 if x == 'A' else 0, s))

print(n) # 3

51) How do you return Multiple Values in Python

In Python, we can return multiple values from a function. Following are different ways

1) Using Object: This is similar to C/C++ and Java, we can create a class (in C, struct) to hold multiple values and return an object of the class.

# A Python program to return multiple values from a method using class
class Test:
def __init__(self):
self.str = "testfortst"
self.x = 20

# This function returns an object of Test
def fun():
return Test()

# Driver code to test above method
t = fun()
print(t.str)
print(t.x)

Output:

testfortst

2) Using Tuple: A Tuple is a comma separated sequence of items. It is created with or without (). Tuples are immutable. See this for details of tuple and list.

# A Python program to return multiple values from a method using tuple

# This function returns a tuple
def fun():
str = "testfortst"
x = 20
return str, x; # Return tuple, we could also
# write (str, x)

# Driver code to test above method
str, x = fun() # Assign returned tuple
print(str)
print(x)

3) Using a list: A list is like an array of items created using square brackets. They are different from arrays as they can contain items of different types. Lists are different from tuples as they are mutable.

# A Python program to return multiple values from a method using list
# This function returns a list
def fun():
str = "testfortst"
x = 20
return [str, x];

# Driver code to test above method
list = fun()
print(list)

Output:

['testfortst',20]

4) Using a Dictionary: A Dictionary is similar to hash or map in other languages. See this for details of dictionary.

# A Python program to return multiple values from a method using dictionary

# This function returns a dictionary

def fun():

d = dict();

d['str'] = "testfortst"

d['x'] = 20

return d

# Driver code to test above method

d = fun()

print(d)

Output:

{'x': 20, 'str': '"testfortst"'}

5) Using Data Class (Python 3.7+): In Python 3.7 and above the Data Class can be used to return a class with automatically added unique methods. The Data Class module has a decorator and functions for automatically adding generated special methods such as __init__() and __repr__() in the user-defined classes.

from dataclasses import dataclass

@dataclass

class Book_list:

name: str

perunit_cost: float

quantity_available: int = 0

# function to calculate total cost

def total_cost(self) -> float:

return self.perunit_cost * self.quantity_available

book = Book_list("Introduction to programming.", 300, 3)

x = book.total_cost()

# print the total cost

# of the book

print(x)

# print book details

print(book)

# 900

Book_list(name='Python programming.',

perunit_cost=200,

quantity_available=3)

Output:

900

Book_list(name='Introduction to programming.', perunit_cost=300, quantity_available=3)

Book_list(name='Python programming.', perunit_cost=200, quantity_available=3)

52)What are different ays to remove duplicates from list

Method 1 : Naive method

In naive method, we simply traverse the list and append the first occurrence of the element in new list and ignore all the other occurrences of that particular element.

# Python 3 code to demonstrate removing duplicated from list using naive methods

# initializing list

test_list = [1, 3, 5, 6, 3, 5, 6, 1]

print ("The original list is : " + str(test_list))

# using naive method to remove duplicated from list

res = []

for i in test_list:

if i not in res:

res.append(i)

# printing list after removal

print ("The list after removing duplicates : " + str(res))

Method 2 : Using list comprehension

This method has working similar to the above method, but this is just a one-liner shorthand of longer method done with the help of list comprehension.

# Python 3 code to demonstrate removing duplicated from list using list comprehension

# initializing list

test_list = [1, 3, 5, 6, 3, 5, 6, 1]

print ("The original list is : " + str(test_list))

# using list comprehension to remove duplicated from list

res = []

[res.append(x) for x in test_list if x not in res]

# printing list after removal

print ("The list after removing duplicates : " + str(res))

Method 3 : Using set()

This is the most popular way by which the duplicated are removed from the list. But the main and notable drawback of this approach is that the ordering of the element is lost in this particular method.

# Python 3 code to demonstrate removing duplicated from list using set()

# initializing list

test_list = [1, 5, 3, 6, 3, 5, 6, 1]

print ("The original list is : " + str(test_list))

# using set() to remove duplicated from list

test_list = list(set(test_list))

# printing list after removal

# distorted ordering

print ("The list after removing duplicates : " + str(test_list))

Method 4 : Using list comprehension + enumerate()
list comprehension coupled with enumerate function can also achieve this task. It basically looks for already occurred elements and skips adding them. It preserves the list ordering.

# Python 3 code to demonstrate removing duplicated from list using list comprehension + enumerate()

# initializing list

test_list = [1, 5, 3, 6, 3, 5, 6, 1]

print ("The original list is : " + str(test_list))

# using list comprehension + enumerate() to remove duplicated from list

res = [i for n, i in enumerate(test_list) if i not in test_list[:n]]

# printing list after removal

print ("The list after removing duplicates : " + str(res))

Method 5 : Using collections.OrderedDict.fromkeys()

This is fastest method to achieve the particular task. It first removes the duplicates and returns a dictionary which has to be converted to list. This works well in case of strings also

# Python 3 code to demonstrate removing duplicated from list

# using collections.OrderedDict.fromkeys()

from collections import OrderedDict

# initializing list

test_list = [1, 5, 3, 6, 3, 5, 6, 1]

print ("The original list is : " + str(test_list))

# using collections.OrderedDict.fromkeys() to remove duplicated from list

res = list(OrderedDict.fromkeys(test_list))

# printing list after removal

print ("The list after removing duplicates : " + str(res))

53)Explain Map,Reduce and filter function?

1) Map() Function

This function takes two arguments. The first argument in the function is the name of function and the second is the sequence or the list.

Syntax: map(func, seq)

Let’s take a look at map() function with example of a list.

a=[1,2,3,4]

b=[2,3,4,5]

c=map(lambda x,y:x+y, a,b)

print(list(c))

Output: [3, 6, 9, 12]

Note: If you don’t print it as a list(c) then chances are there that output will be printed as a map object. So you have to print it as a list.

Like the above example you can also evaluate some more mathematical expressions and check the list as a boolean output. For example, make a list with number divisible and non-divisible by 2. Now add that condition in the lambda function expression and then get the output as a list. You’ll find that it prints true and false output.

2) Filter() Function

Like map() function this filter() function also takes two arguments – func and list. Let’s take an example to see how the filter() function works.

b=[2,3,4,9]

c=filter(lambda x:x%3==0,b)

print(list(c))

Output: 3,9

You see filter() function removes the list items that are not divisible by 3. It only displays the two items that qualifies for the same. So the list argument in the filter function only returns value that are true as per the condition.

3) Reduce() function

Reduce function is not available in python 3.x. You can skip this section if you’re using the new version of python. In case if you wish to use this function, you can use functools.reduce() instead. Reduce() function takes two arguments and the seq/list item continually evaluates until the last item. This way the list/sequence is reduced as per the arithmetical expression condition.

Let’s take a look at example to see how it works.

a=[1,2,3,4]

reduce(lambda x,y:x>y, a)

Output: false

This sums up our small tutorial on python lambda functions. You can keep tab on python 3.x version updates to see changes to the lambda functions.

54) Explain Underscore (_) in Python

Following are different places where _ is used in Python:

A. Single Underscore:

In Interpreter
After a name
Before a name

B. Double Underscore:

__leading_double_underscore
__before_after__

A.Single Underscore

In Interpreter:

_ returns the value of last executed expression value in Python Prompt/Interpreter

>>> a = 10
>>> b = 10
>>> _ 
Traceback (most recent call last): 
File "<stdin>", line 1, in <module> 
NameError: name '_' is not defined 
>>> a+b 
20
>>> _ 
20
>>> _ * 2
40
>>> _ 
40
>>> _ / 2
20

For ignoring values:

Multiple time we do not want return values at that time assign those values to Underscore. It used as throwaway variable.

# Ignore a value of specific location/index 
for _ in range(10) 
    print ("Test") 
  
# Ignore a value when unpacking 
a,b,_,_ = my_method(var1) 

After a name

Python has their by default keywords which we can not use as the variable name. To avoid such conflict between python keyword and variable we use underscore after name

>>> class MyClass(): 
...     def __init__(self): 
...             print ("OWK") 
  
>>> def my_defination(var1 = 1, class_ = MyClass): 
...     print (var1) 
...     print (class_) 
  
>>> my_defination() 
1
__main__.MyClass 
>>> 

Before a name

Leading Underscore before variable/function/method name indicates to programmer that It is for internal use only, that can be modified whenever class want.

Here name prefix by underscore is treated as non-public. If specify from Import * all the name starts with _ will not import. Python does not specify truly private so this ones can be call directly from other modules if it is specified in __all__, We also call it weak Private

class Prefix: 
...     def __init__(self): 
...             self.public = 10
...             self._private = 12
>>> test = Prefix() 
>>> test.public 
10
>>> test._private 
12

Python class_file.py

def public_api(): 
    print ("public api") 
  
def _private_api(): 
    print ("private api") 

Calling file from Prompt

>>> from class_file import *
>>> public_api() 
public api 
  
>>> _private_api() 
Traceback (most recent call last): 
File "<stdin>", line 1, in <module> 
NameError: name '_private_api' is not defined 
  
>>> import class_file 
>>> class_file.public_api() 
public api 
>>> class_file._private_api() 
private api 

B. Double Underscore(__)

__leading_double_underscore

Leading double underscore tell python interpreter to rewrite name in order to avoid conflict in subclass. Interpreter changes variable name with class extension and that feature known as the Mangling.

testFile.py

class Myclass(): 
    def __init__(self): 
        self.__variable = 10

Calling from Interpreter

>>> import testFile 
>>> obj = testFile.Myclass() 
>>> obj.__variable 
Traceback (most recent call last): 
File "", line 1, in
AttributeError: Myclass instance has no attribute '__variable'
nce has no attribute 'Myclass'
>>> obj._Myclass__variable 
10

In Mangling python interpreter modify variable name with ___. So Multiple time It use as the Private member because another class can not access that variable directly. Main purpose for __ is to use variable/method in class only If you want to use it outside of the class you can make public api

class Myclass(): 
    def __init__(self): 
        self.__variable = 10
    def func(self) 
        print (self.__variable)

Calling from Interpreter

>>> import testFile 
>>> obj = testFile.Myclass() 
>>> obj.func() 
10

__BEFORE_AFTER__
Name with start with __ and ends with same considers special methods in Python. Python provide this methods to use it as the operator overloading depending on the user.

Python provides this convention to differentiate between the user defined function with the module’s function

class Myclass(): 
    def __add__(self,a,b): 
        print (a*b) 

Calling from Interpreter

>>> import testFile 
>>> obj = testFile.Myclass() 
>>> obj.__add__(1,2) 
2
>>> obj.__add__(5,2) 
10

Networking Interview Questions - for Testers

2021-04-17T06:56:00.028-07:00

Basics of Network Communication
For a network to exist, we need a minimum of two connected devices.

Network communication happens at different levels or layers (OSI model and TCP/IP model)
Each layer of network communication is responsible for passing the information on to the next layer in the stack.
Data transferred between layers is known as a Protocol Data Unit (PDU).
These network layers of communication allow for better troubleshooting.
The rise of the internet and new technology has changed the way devices communicate with each other and thus may require new protocols.

What is a reverse proxy?

A proxy is a server that accepts connections from clients, which actively configured the proxy server on their machines, in their network settings.
When a client makes a connection to a server, the requests always pass through that proxy server.
Companies and organizations can set up proxy servers to filter connections, provide more security, and log traffic. Without using the proxy, clients can’t reach the outside network. Proxy servers are also useful to provide privacy and avoid network restrictions imposed by countries governments.
A reverse proxy on the other hand is set up by the server. It’s completely transparent to clients, they don’t know this middleman exists, but it does a very useful job on the servers, filtering requests and sending them to the appropriate service that handles them
It’s common to use Nginx as a reverse proxy, and have services written for example in Node.js listening on internal ports, inaccessible from the outside.

Network Protocol Terminologies

LAN: LAN stands for “Local Area Network” and refers to a network that is not publicly accessible by the internet. Examples of this are home or office network.

WAN: WAN stands for “Wide Area Network” and generally refers to large dispersed networks and, more broadly, the internet.

ISP: ISP stands for “Internet Service Provider” and refers to the company responsible for providing you access to the internet.

NAT: Network Address Translation allows requests from outside your local network to be mapped to devices within your local network.

Firewall: A firewall is a piece of hardware or software that enforces what type of network traffic is and is not allowed. This is generally done by establishing rules for which ports should be externally accessible.

Router: A router is a network device whose main goal is to transfer data back and forth between different networks. This device allows requests to be made to the internet and for information to be sent back to the devices on a local network.

Switch: The basic function of a switch is to provide access between devices on a local network. An example is an Ethernet switch.

Network Interface: This component allows you to connect to a public or private network. It provides the software required to utilize networking hardware. An example of this is the Network Interface Cards (NICs).

Port: A port is a logically defined connection location. Ports provide a destination endpoint for communication and the transfer of data. The ports range from 0 to 65535.

Packet: A packet is the basic unit of data transferred over a network. A packet has a header that gives information about the packet (source, destination, etc) and a body or payload containing the actual data being sent.

What happens when you type something into the Google search box and press enter”.

I analyze URL requests only

Modern browsers have the capability of knowing if the thing you wrote in the address bar is an actual URL or a search term, and they will use the default search engine if it’s not a valid URL.
I assume you type an actual URL.
When you enter the URL and press enter, the browser first builds the full URL.
If you just entered a domain, like testing.com, the browser by default will prepend HTTP:// to it, defaulting to the HTTP protocol.

DNS Lookup phase

The browser starts the DNS lookup to get the server IP address.
The domain name is a handy shortcut for us humans, but the internet is organized in such a way that computers can look up the exact location of a server through its IP address, which is a set of numbers like 222.324.3.1 (IPv4).
First, it checks the DNS local cache, to see if the domain has already been resolved recently.
Chrome has a handy DNS cache visualizer you can see at chrome://net-internals/#dns
If nothing is found there, the browser uses the DNS resolver, using the gethostbyname POSIX system call to retrieve the host information.

gethostbyname

gethostbyname first looks in the local hosts file, which on macOS or Linux is located in /etc/hosts, to see if the system provides the information locally.

If this does not give any information about the domain, the system makes a request to the DNS server.

The address of the DNS server is stored in the system preferences.

Those are 2 popular DNS servers:

8.8.8.8: the Google public DNS server
1.1.1.1: the CloudFlare DNS server

Most people use the DNS server provided by their internet provider.

The browser performs the DNS request using the UDP protocol.

TCP and UDP are two of the foundational protocols of computer networking. They sit at the same conceptual level, but TCP is connection-oriented, while UDP is a connectionless protocol, more lightweight, used to send messages with little overhead.

How the UDP request is performed is not in the scope of this tutorial

The DNS server might have the domain IP in the cache. If not, it will ask the root DNS server. That’s a system (composed of 13 actual servers, distributed across the planet) that drives the entire internet.
The DNS server does not know the address of each and every domain name on the planet.
What it knows is where the top-level DNS resolvers are.
A top-level domain is the domain extension: .com, .it, .pizza and so on.
Once the root DNS server receives the request, it forwards the request to that top-level domain (TLD) DNS server.
Say you are looking for flaviocopes.com. The root domain DNS server returns the IP of the .com TLD server.
Now our DNS resolver will cache the IP of that TLD server, so it does not have to ask the root DNS server again for it.
The TLD DNS server will have the IP addresses of the authoritative Name Servers for the domain we are looking for.

How? When you buy a domain, the domain registrar sends the appropriate TDL the name servers. When you update the name servers (for example, when you change the hosting provider), this information will be automatically updated by your domain registrar.

Those are the DNS servers of the hosting provider. They are usually more than 1, to serve as backup.

For example:

ns1.dreamhost.com
ns2.dreamhost.com
ns3.dreamhost.com

The DNS resolver starts with the first, and tries to ask the IP of the domain (with the subdomain, too) you are looking for.

That is the ultimate source of truth for the IP address.

Now that we have the IP address, we can go on in our journey.

TCP request handshaking

With the server IP address available, now the browser can initiate a TCP connection to that.
A TCP connection requires a bit of handshaking before it can be fully initialized and you can start sending data.
Once the connection is established, we can send the request

Sending the request

The request is a plain text document structured in a precise way determined by the communication protocol.

It’s composed of 3 parts:

the request line
the request header
the request body

The request line

The request line sets, on a single line:

the HTTP method
the resource location
the protocol version

Example:

GET / HTTP/1.1

The request header

The request header is a set of field: value pairs that set certain values.

There are 2 mandatory fields, one of which is Host, and the other is Connection, while all the other fields are optional:

Host: testing.com

Connection: close

Host indicates the domain name which we want to target, while Connection is always set to close unless the connection must be kept open.

Some of the most used header fields are:

Origin
Accept
Accept-Encoding
Cookie
Cache-Control
Dnt

but many more exist.

The header part is terminated by a blank line.

The request body

The request body is optional, not used in GET requests but very much used in POST requests and sometimes in other verbs too, and it can contain data in JSON format.

Since we’re now analyzing a GET request, the body is blank and we’ll not look more into it.

The response

Once the request is sent, the server processes it and sends back a response.

The response starts with the status code and the status message. If the request is successful and returns a 200, it will start with:

200 OK

The request might return a different status code and message, like one of these:

404 Not Found

403 Forbidden

301 Moved Permanently

500 Internal Server Error

304 Not Modified

401 Unauthorized

The response then contains a list of HTTP headers and the response body (which, since we’re making the request in the browser, is going to be HTML)

Parse the HTML

The browser now has received the HTML and starts to parse it, and will repeat the exact same process we did for all the resources required by the page:

CSS files
images
the favicon
JavaScript files

What protocol is used by DNS name servers?

DNS uses UDP for communication between servers. It is a better choice than TCP because of the improved speed a connectionless protocol offers. Of course, transmission reliability suffers with UDP.

Explain difference between ARP and RARP

The address resolution protocol (ARP) is used to associate the 32 bit IP address with the 48 bit physical address, used by a host or a router to find the physical address of another host on its network by sending a ARP query packet that includes the IP address of the receiver. The reverse address resolution protocol (RARP) allows a host to discover its Internet address when it knows only its physical address.

Explain ICMP

ICMP is Internet Control Message Protocol, a network layer protocol of the TCP/IP suite used by hosts and gateways to send notification of datagram problems back to the sender. It uses the echo test / reply to test whether a destination is reachable and responding. It also handles both control and error messages.

What are the data units at different layers of the TCP / IP protocol suite

The data unit created at the application layer is called a message, at the transport layer the data unit created is called either a segment or an user datagram, at the network layer the data unit created is called the datagram, at the data link layer the datagram is encapsulated in to a frame and finally transmitted as signals along the transmission media

What is Network Scanning?

Network scanning refers to the process of obtaining additional information and performing a more detailed reconnaissance based on the collected information in the foot printing phase.
In this phase, a number of different procedures are used with the objective to identify hosts, ports, and services in the target network. The whole purpose is to identify vulnerabilities in communication channels and then create an attack plan.

Types of Network Scanning

Scanning has three types:

Port scanning - used to list open ports and services
Network scanning - used to list IP addresses
Vulnerability scanning - used to discover the presence of known vulnerabilities

Scanning Techniques

Port scanning techniques are extremely useful when it comes to identifying open ports. Scanning techniques represent different categories which are used based on protocol types. They are categorized into three categories:

Scanning ICMP network services
Scanning TCP network services
Scanning UDP network services

Scanning ICMP network services

1) ICMP Scanning

ICMP scanning is used for identifying active devices and determining whether ICMP can pass through a firewall.

2) Ping Sweep

Ping sweep is used to determine the range of IP addresses that is mapped to active devices. It allows hackers to calculate subnet masks and identify the number of present hosts in the subnet. This in turn enables them to create an inventory of active devices in the subnet.

3) ICMP Echo Scanning

ICMP Echo Scanning is used to determine which hosts are active in a target network by pinging all the machines in the network.

Scanning TCP Network Services

1) TCP Connect

TCP connect scan used for detecting open ports upon the completion of the three-way handshake. It works by establishing a full connection and then dropping it by sending a RST packet.

2) Stealth Scan

Stealth scan is used for bypassing firewall and logging mechanisms. It works by resetting the TCP connection before the three-way handshake is completed, which in turn makes the connection half open.

3) Inverse TCP Flag Scanning

Inverse TCP flag scanning works by sending TCP probe packets with or without TCP flags. Based on the response, it is possible to determine whether the port is open or closed. If there is no response, then the port is open. If the response is RST, then the port is closed.

4) Xmas Scan

Xmas scan works by sending a TCP frame with FIN, URG, and PUSH flags set to the target device. Based on the response, it is possible to determine whether the port is open or closed. If there is no response, then the port is open. If the response is RST, then the port is closed. It is important to note that this scan works only for UNIX hosts.

5) ACK Flag Probe Scanning

ACK flag probe scanning works by sending TCP probe packets with ACK flag set in order to determine whether the port is open or closed. This is done by analyzing the TTL and WINDOW field of the received RST packet’s header. The port is open if the TTL value is less than 64.

Similarly, the port is also considered to be open if the WINDOW value is not 0 (zero). Otherwise, the port is considered to be closed.

ACK flag probe is also used to determine the filtering rules of the target network. If there is no response, then that means that a stateful firewall is present. If the response is RST, then the port is not filtered.

Scanning UDP Network Services

1) IDLE/IPID Header Scan

IDLE/IPID header scan works by sending a spoofed source address to the target to determine which services are available. In this scan, hackers use IP address of a zombie machine for sending out the packets. Based on the IPID of the packer (fragment identification number), it is possible to determine whether the port is open or closed.

2) UDP Scanning

UDP scanning uses UDP protocol to test whether the port is open or closed. In this scan there is no flag manipulation. Instead, ICMP is used to determine if the port is open or not. So, if a packet is sent to a port and the ICMP port unreachable packet is returned, then that means that the port is closed. If, however, there is no response, then the port is open.

3) SSDP and List Scanning

SSDP, or Simple Service Discovery Protocol, service responds to queries sent over IPv4 and IPv6 broadcast addresses. Attackers use this scan to exploit UPnP vulnerabilities and carry out buffer overflow or DoS attacks. List scanning indirectly discovers hosts. This scan works by listing out IP addresses and names without pinging the hosts and with performing a reverse DNS resolution to identify the names of the hosts.

What is a port?

When making network requests, you use an IP address, or a host name, and a port.

Like this:

http://localhost:8080 (port 8080)

ftp://127.0.0.1:29392 (port 29392)

What is a port, exactly?

It’s a technique introduced to allow multiple applications to respond on the same computer, on the same protocol.

For example we might have a web server running on our machine. A second web server can be started on a different port.

Say the first runs on port 80, which is the default for web servers using the HTTP protocol. The same can run on any other port except port 80. It’s common to use port 8080 or port 81, for example.

HTTPS runs on port 443 by default.

Every protocol has a different default port, but programs are not required to use that. They can use any unused port between 1 and 65535 (16 bits unsigned = 2^16). Here is a list of default port numbers for all protocols based on TCP and UDP.

Historically:

FTP uses 21

Telnet uses 23

SMTP uses 25

POP3 uses 110

HTTP vs HTTPS

HTTP (Hyper Text Transfer Protocol) is the protocol that powers the web as we know it.

It sits on top of TCP, which sits on top of IP.

Web pages can either use HTTP or HTTPS (Hyper Text Transfer Protocol Secure).

How are they different? And, why is now HTTP being marked as non-secure by Chrome?

Security

When you request an HTTP page from a server, the data goes through many different networks, each controlled by a separate company or entity.

Starting from the WiFi router, which might be owned by the coffee shop or by the city public network infrastructure, every single node in the network can see the request and the response, and modify it in any way.

They might inject ads, they might inject malware, they might log any credentials you enter. A server in the middle can play as a man-in-the-middle, sending compromised information.

This also applies to any internet protocol that’s not secured.

HTTPS traffic is end-to-end encrypted, and this means there is nothing in between that can read the information exchanged between you and the server at the other side of the network.

The ports

By default, HTTP is served on port 80, while HTTPS is served on port 443. Those are the default ports, but a web server can choose to serve content on a different, random port, in which case you need to specify it in the address bar:

http://flaviocopes.com

http://flaviocopes.com:80/javascript

https://flaviocopes.com:8081/javascript

Is HTTPS slower?

No! It’s the opposite.

There is a myth around page speed. People think that the TLS handshake required for HTTPS is making page speed slower, but in reality, an HTTPS page can load up way, way faster than HTTP.

Why? Because of HTTP/2, the newest version of the HTTP protocol. HTTP/2 can serve requests in parallel, and requires a secure connection, so if your server uses a modern Web Server, which supports HTTP/2, then your web pages are going to have a significant speed bump when using HTTPS.

HTTP/2 introduces better parallelism, multiplexing, and compression, and that is an awesome update to HTTP.

Does HTTPS affect SEO?

Yes.

In particular, Google says HTTPS is going to give you an advantage in SEO terms.

Also, Google is going to officially mark HTTP sites as non-secure in its Chrome browser, and this is clearly an indication that if you care what Google wants, and you want to take advantage of that, you should switch to HTTPS, as soon as possible. The best possible time would have been 3 years ago, the next best time is today.

Is HTTPS difficult to implement?

Not at all. Thanks to free SSL certificates provided by Let’s Encrypt, the push for HTTPS had a huge impact and how every decent hosting provider is implementing it for free on all the accounts. Thanks to this, in 2018 HTTPS connections were more than the HTTP connections.

In the past having an SSL certificate for your site was a premium option that few were willing to purchase for a regular site, that was not making money or didn’t process user data.

The TCP Protocol

TCP means Transfer Control Protocol, and it’s the basis of the Web and other applications like Email.
TCP sits on top of the Internet Protocol (IP) and builds a base system upon which application-level protocols like HTTP, FTP, IMAP and many others.
TCP, contrary to IP and UDP, is connection oriented.
Before transmission can happen over TCP, a connection must be established. Data is sent, in form of little packets, and when the communication ends the connection is closed.
When data is transmitted over TCP, there’s a relatively complex workflow called handshake that must happen.
Handshake allows the end-to-end connection to happen, and this makes sure TCP can provide one of its peculiar features: reliability. Using TCP, we can always know if a packet the sender sent was received correctly by the receiver.
If a packet gets lost, the protocol is able to handle it and the packet is re-sent.
On the IP protocol, connections happen from computer to computer. In TCP, a connection happens form process to process, using a the concept of ports.
The port, associated to an IP address, allows to uniquely identify a process on a computer. Like this:

localhost:8080

google.com:1234

Each application protocol has a default port. For example HTTP has 80, HTTPS has 443 and FTP has 21. This is why you don’t usually have to specify the port, in the browser.
Programs are not required to use the default, this is why especially on your local computer, you might see ports like 1313 or 8080 when you start a new application.
Port numbers range from 1 to 65535 (the port number is a 16 bits unsigned, which corresponds to 2^16 possible values).

The UDP Protocol

UDP, User Datagram Protocol, is a transfer protocol, an alternative to TCP.
Its main difference from TCP is that it’s connectionless.
This implies that it’s faster, each packet sent is more lightweight, as it does not contain all the information needed in TCP, and it does have a lighter handshake process.
The drawback is that UDP is not reliable as TCP.
In TCP, if a packet gets lost, the protocol is able to handle it and the packet is re-sent.
In UDP, this is not built-in into the protocol, and must be handled at a higher level (built on top of it). There is no built-in check to control if a packet was received, and if it is received correctly.
Some of the most notable application protocols that rely on the UDP layer are DNS and DHCP, and more importantly is the base layer of HTTP/3, the next version of HTTP.
The UDP protocol uses ports to allow communication between processes, like with TCP.

How traceroute (or tracert) works?

Tracert are both command line utilities that are built into Windows

(traceroute and ping for Linux operating systems) computer systems.

Syntax : tracecert "hostname"

Discover the path: Tracert sends an ICMP echo packet, but it takes advantage

of the fact that most Internet routers will send back an ICMP ‘TTL expired in

transit’ message if the TTL field is ever decremented to zero by a router. Using

this knowledge, we can discover the path taken by IP Packets.

How tracert works: Tracert sends out an ICMP echo packet to the named host,

but with a TTL of 1; then with a TTL of 2; then with a TTL of 3 and so on.

Tracert will then get ‘TTL expired in transit’ message back from routers until the

destination host computer finally is reached and it responds with the standard

ICMP ‘echo reply’ packet.

Round Trip Times: Each millisecond (ms) time in the table is the round-trip

time that it took (to send the ICMP packet and to get the ICMP reply packet).

The faster (smaller) the times the better, ms times of 0 mean that the reply was

faster than the computers timer of 10 milliseconds, so the time is actually

somewhere between 0 and 10 milliseconds

Packet Loss: Packet loss kills throughput. So, having no packet loss is critical to

having a connection to the Internet that responds well. A slower connection with

zero packet loss can easily outperform a faster connection with some packet loss.

Also, packet loss on the last hop, the destination, is what is most important.

Sometimes routers in-between will not send ICMP ‘TTL expired in transit’

messages, causing what looks to be high packet loss at a particular hop, but all it

means is that the particular router is not responding to ICMP echo.

Which port number would you open on a firewall to allow access to a Windows

remote desktop server on the LAN network.

Windows remote desktop servers work on TCP port 3389, which should be opened on

the firewall for access.

What is a network / subnet mask? Explain how host A sends a message / packet to

host B when: (a) both are on same network and (b) both are on different networks.

Explain which layer makes the routing decision and how.

A mask is a bit pattern used to identify the network/subnet address. The IP address consists

of two components: the network address and the host address.

The IP addresses are categorized into different classes which are used to identify the network

address.

Example: Consider IP address 152.210.011.002. This address belongs to Class B, so:

Network Mask: 11111111.11111111.00000000.00000000
Given Address: 10011000.11010101.00001011.00000010

By ANDing Network Mask and IP Address, we get the following network address:

10011000.11010101.00000000.00000000 (152.210.0.0)
Host address: 00001011.00000010

Similarly, a network administrator can divide any network into sub-networks by using subnet

mask. To do this, we further divide the host address into two or more subnets.

For example, if the above network is divided into 18 subnets (requiring a minimum of 5 bits

to represent 18 subnets), the first 5 bits will be used to identify the subnet address.

Subnet Mask: 11111111.11111111.11111000.00000000 (255.255.248.0)
Given Address: 10011000.11010101.00001011.00000010

So, by ANDing the subnet mask and the given address, we get the following subnet address:

10011000.11010101.00001000.00000000 (152.210.1.0)

How Host A sends a message/packet to Host B:

When both are on same network: the host address bits are used to identify the host within the network.
Both are on different networks: the router uses the network mask to identify the network and route the packet. The host can be identified using the network host address.
The network layer is responsible for making routing decisions. A routing table is used to store the path information and the cost involved with that path, while a routing algorithm uses the routing table to decide the path on which to route the packets.
Routing is broadly classified into Static and Dynamic Routing based on whether the table is fixed or it changes based on the current network condition.

Name two reasons as to why ping response is not received from the destination

The ping can fail if the destination is shutdown or it can also be a firewall on the

destination blocking the packet.

Explain a technique by which web access can be blocked on a network with a

firewall.

An ACL can be configured which would block DNS packets originating from the

network. DNS is used for resolving URL into IP address. If DNS is blocked, web

communication would fail

Does HTTPS use TLS/SSL protocol at the transport layer

HTTPS uses TCP at the transport layer. TCP port 443 is used. TLS/SSL is used by

HTTPS for encrypting the data exchanged.

Can two vlans be assigned with two subnets from the same major network.

Vlans are used for segregating networks. So two subnets irrespective of whether they

are from the same of different major networks can be used with two vlans.

Explain what happens, step by step, after you type a URL into a browser. Use as much

detail as possible.

There’s no right, or even complete, answer for this question. This question allows you to go

into arbitrary amounts of detail depending on what you’re comfortable with. Here’s a start

though:

1. Browser contacts the DNS server to find the IP address of URL.

2. DNS returns back the IP address of the site.

3. Browser opens TCP connection to the web server at port 80.

4. Browser fetches the html code of the page requested.

5. Browser renders the HTML in the display window.

6. Browser terminates the connection when window is closed

One of the most interesting steps is Step 1 and 2 - “Domain Name Resolution.” The web addresses we type are nothing but an alias to an IP address in human readable form. Mapping of domain names and their associated Internet Protocol (IP) addresses is managed by the Domain Name System (DNS), which is a distributed but hierarchical entity.

Each domain name server is divided into zones. A single server may only be responsible for

knowing the host names and IP addresses for a small subset of a zone, but DNS servers can

work together to map all domain names to their IP addresses. That means if one domain

name server is unable to find the IP addresses of a requested domain then it requests the

information from other domain name servers.

What are the differences between TCP and UDP? Explain how TCP handles reliable

delivery (explain ACK mechanism), flow control (explain TCP sender’s / receiver’s window) and congestion control.

TCP (Transmission Control Protocol): TCP is a connection-oriented protocol. A connection can

be made from client to server, and from then on any data can be sent along that connection.

Reliable - when you send a message along a TCP socket, you know it will get there unless the connection fails completely. If it gets lost along the way, the server will re-request the lost part. This means complete integrity; data will not get corrupted.
Ordered - if you send two messages along a connection, one after the other, you know the first message will get there first. You don’t have to worry about data arriving in the wrong order.
Heavyweight - when the low level parts of the TCP “stream” arrive in the wrong order, resend requests have to be sent. All the out of sequence parts must be put back together, which requires a bit of work.

UDP(User Datagram Protocol): UDP is connectionless protocol. With UDP you send messages

(packets) across the network in chunks.

Unreliable - When you send a message, you don’t know if it’ll get there; it could get lost on the way.
Not ordered - If you send two messages out, you don’t know what order they’ll arrive in.
Lightweight - No ordering of messages, no tracking connections, etc. It’s just fire and forget! This means it’s a lot quicker, and the network card / OS have to do very little work to translate the data back from the packets

Which protocol would you block on a firewall for blocking tracert

Tracert uses ICMP at the network layer. ICMP should be denied on a firewall to block

tracert.

Which is the protocol used by both traceroute and ping

ICMP is used by both the protocols at the network layer.

Name one technique which can be used for identifying existing IP addresses on a

LAN network.

NMAP which is a scanning tool can be used to perform a scan on the network which

would display the list of available IP addresses on the network. NMAP arp ping scan

can be used for the same.

Can the username and password sent from a HTTP client be viewed in clear text

on the server.

HTTP does not encrypt data. This would cause the username and password to be

viewed in clear text on the server

Can a FTP server installed on Linux accessed by a FTP client on Windows.

FTP is a TCP/IP protocol. TCP/IP is a vendor neutral protocol. So a FTP client on

Windows can access the FTP server which is installed on Linux

How can the number of TCP connections be viewed on a Windows system.

netstat command can be used for the purpose. The command netstat –p tcp would

display all tcp connections on the system

Explain how access to FTP server on a network can be restricted using a firewall.

An access control list can be configured on the firewall which would block access to

FTP server ports which are TCP port 20 and 21.

How do two computers connected to a switch communicate with each other.

An IP header with the source and destination IP address as IP1 and IP2 is created. PC1 sends an ARP request frame to find the mac-address of PC2. This is required to construct the ethernet frame to encapsulate the IP packet. After the mac-address of PC2 is received, the frame is constructed and the IP packet encapsulated. The frame is sent to the switch and is

received on port on E0. The switch looks into the destination mac-address in the frame,

which is PC2’s mac-address and checks if the entry is available in it’s mac-address table. If yes, the frame is forwarded to the port on which PC2 is connected. If unavailable, the switch floods the frame to all ports. After PC2, receives the frame, it looks into the destination mac-address to check if the frame is intended for itself. Once verified, the destination IP address is verified with it’s own IP address. As it is a match, the ping packet is processed and the response to the ping packet created. The response packet would contain the source IP address as IP2 and the destination IP address as IP1, and a new frame would be created with the source and destination mac-address as PC2 and PC1 respectively.

How do computers connected to two different switches communicate.

PC1 and PC2 are connected to respective ports on the switch. The switches are connected to each other using the E1 ports on the respective switches. When PC1 pings PC2, an ARP request packet is generated, for identifying the mac-address of PC2. The ARP request packet is a broadcast packet, which is broadcasted to all ports on SW1. The ARP packet would be sent through the E1 interface on SW1, reach the E1 interface on SW2 and eventually reach PC2. PC2 would respond with it’s mac-address to PC1. Now on SW2, the mac-address of PC1 is added to the E1 interface on SW2, as it had received the ARP request through the interface, which had the source mac-address as that of PC1. This information would be updated in the cam table of SW1. The ARP reply would be sent out through E1 on

SW2 and E1 on SW1 and eventually would reach PC1. The next time PC1 pings PC2, the cam table of the switch would list the mac-address of PC1 on E1 on SW1. All packets would be sent to E1 on SW1, which would then be forwarded out to SW2

Name two techniques by which a single internet connection can be shared by

multiple users on a LAN.

The requirement can be achieved by the use of NAT router (Network address

translation) or a proxy server.

Name two protocols which are vulnerable to brute force attacks.

Telnet and FTP are two protocols which are vulnerable to brute force attacks.

What is a Routing Table?

Think of a routing table like a map or a set of directions for your computer or router to figure out where to send data on the internet.

Imagine your computer wants to send a message to a friend's computer. It doesn't know exactly where your friend's computer is, but it knows some general areas.

Routing Table Entries: The routing table is like a list of places or neighborhoods your computer knows about. Each entry in the table represents a place your computer can send data to. These places are either specific locations or general areas on the internet.
Destination Addresses: Your computer looks at the address of your friend's computer and compares it to the entries in the routing table. It's like checking if your friend lives in one of the neighborhoods listed.
Next-Hop Directions: When your computer finds a match in the routing table, it also sees directions to the next "stop" on the way to your friend's computer. This next stop is usually a router or gateway device that knows how to get closer to the final destination.
Choosing the Best Route: Your computer picks the routing table entry that matches the most digits in your friend's address. It's like choosing the neighborhood that's the closest match. This is called "longest prefix match."
Sending the Data: Your computer sends the data to the next-hop router/gateway according to the directions in the routing table entry. The router then looks at its own routing table to figure out where to send the data next.

In a nutshell, a routing table is like a list of places your computer knows about on the internet, along with directions on how to get there. It helps your computer make smart decisions about where to send data, even if it doesn't know the exact location of the destination.

A routing table is a data structure used in computer networking to store information about the paths that data packets should take to reach their destination. It is a crucial component of routers and network devices responsible for forwarding data traffic between different networks or subnetworks.

where do we keep routing table details

Routing table details are typically stored in the memory of networking devices like routers and switches. These devices use routing tables to determine how to forward data packets from one network or host to another. Here's where you'll find routing table details:

Router's Memory: Routers are key networking devices responsible for forwarding data between different networks. Each router maintains its own routing table, which is stored in its memory (RAM). This routing table contains information about routes to various destinations, next-hop routers, and associated metrics.
Switches: Layer 3 switches, which can perform routing functions in addition to traditional switching, also have routing tables. These routing tables are stored in the device's memory and are used to make decisions about how to route traffic between different subnets or VLANs.
Operating Systems: In the case of host devices (computers, servers, etc.), routing tables are managed by the operating system. When you run a command like "route print" (Windows) or "netstat -r" (Unix/Linux) in a command prompt or terminal, you can view the routing table for that specific host. These routing tables help the host determine where to send network traffic.
Networking Equipment Configuration: Network administrators configure and manage routing tables on routers and switches. They use various protocols and commands to add, modify, or delete routing table entries. These configurations are often stored in the device's configuration files.
Dynamic Routing Protocols: In many cases, routing tables are not static but dynamically updated based on the network's topology and changes. Dynamic routing protocols (e.g., OSPF, BGP, RIP) enable routers to exchange routing information with their neighboring routers, allowing the tables to adapt to network changes automatically.
Routing Table Cache: Routing devices often maintain a routing table cache to speed up the routing process. This cache stores recently used routing information, allowing routers to make routing decisions more quickly. The cache is kept in memory and is updated as needed.

However, in most cases, routing table information is stored in the device's memory and can be accessed and manipulated through the device's configuration interface or command-line interface.

C:\Users\user1>route print

===========================================================================

Interface List

16...c8 4b d6 43 62 a1 ......Intel(R) Ethernet Connection (16) I219-LM

8...3c 21 9c e3 8d 1c ......Microsoft Wi-Fi Direct Virtual Adapter

18...3e 21 9c e3 8d 1b ......Microsoft Wi-Fi Direct Virtual Adapter #2

4...3c 21 9c e3 8d 1b ......Intel(R) Wi-Fi 6E AX211 160MHz

19...3c 21 9c e3 8d 1f ......Bluetooth Device (Personal Area Network)

1...........................Software Loopback Interface 1

===========================================================================

IPv4 Route Table

===========================================================================

Active Routes:

Network Destination Netmask Gateway Interface Metric

0.0.0.0 0.0.0.0 192.168.0.1 192.168.0.104 50

127.0.0.0 255.0.0.0 On-link 127.0.0.1 331

127.0.0.1 255.255.255.255 On-link 127.0.0.1 331

127.255.255.255 255.255.255.255 On-link 127.0.0.1 331

192.168.0.0 255.255.255.0 On-link 192.168.0.104 306

192.168.0.104 255.255.255.255 On-link 192.168.0.104 306

192.168.0.255 255.255.255.255 On-link 192.168.0.104 306

224.0.0.0 240.0.0.0 On-link 127.0.0.1 331

224.0.0.0 240.0.0.0 On-link 192.168.0.104 306

255.255.255.255 255.255.255.255 On-link 127.0.0.1 331

255.255.255.255 255.255.255.255 On-link 192.168.0.104 306

===========================================================================

Persistent Routes:

None

IPv6 Route Table

===========================================================================

Active Routes:

If Metric Network Destination Gateway

1 331 ::1/128 On-link

4 306 fe80::7b01:698c:f8c2:a4a5/128

On-link

1 331 ff00::/8 On-link

4 306 ff00::/8 On-link

===========================================================================

Persistent Routes:

None

C:\Users\user1>

SQL for testers

2021-04-15T06:15:00.020-07:00

SQL Queries Set 1

1.Display the dept information from department table
select * from dept;

2.Display the details of all employees
select * from emp;

3.Display the name and job for all employees
select ename,job from emp;

4.Display name and salary for all employees
select ename,sal from emp;

5.Display employee number and total salary for each employee
select empno,sal+comm from emp;

6.Display employee name and annual salary for all employees
select empno,ename,12*sal+nvl(comm,0) annualsal from emp;

7.Display the names of all employees who are working in department number 10
select ename from emp where deptno = 10;

8.Display the names of all employees working as clerks and drawing a salary more than 3000
select ename from emp wher job = ‘CLERK’ and sal > 3000;

9.Display employee number and names for employees who earn commission
select empno,ename from emp where comm is not null and comm > 0;

10.Display names of employees who do not earn any commission
select empno,ename from emp where comm is null and comm = 0;

11.Display the names of employees who are working as clerk , salesman or analyst and drawing a salary more than 3000
select ename from emp where (job=’CLERK’ or job=’SALESMAN’ or job=’ANALYST’) and sal>3000;

12.Display the names of employees who are working in the company for the past 5 years
select ename from emp where sysdate – hiredate > 5*365;

13.Display the list of employees who have joined the company before 30 th june 90 or after 31 st dec 90
select * from emp where hiredate between ’30-jun-1990′ and ’31-dec-1990′;

14.Display current date
select sysdate from dual;

15.Display the list of users in your database (using log table)
select * from dba_users;

16.Display the names of all tables from the current user
select * from tab;

17.Display the name of the current user
show user;

18.Display the names of employees working in department number 10 or 20 or 40 or employees working as clerks , salesman or analyst
select ename from emp where deptno in (10,20,40) or job in (‘CLERK’,’SALESMAN’,’ANALYST’);

19.Display the names of employees whose name starts with alphabet S
select ename from emp where ename like ‘S%’;

20.Display employee name from employees whose name ends with alphabet S
select ename from emp where ename like ‘%S’;

21.Display the names of employees whose names have sencond alphabet A in their names
select ename from emp where ename like ‘_S%’;

22.Display the names of employees whose name is exactly five characters in length
select ename from emp where length(ename)=5;
or
select ename from emp where ename like ‘_____’;

23.Display the names of employees who are not working as managers
select * from emp minus (select * from emp where empno in (select mgr from emp));
or
select * from emp where empno not in (select mgr from emp where mgr is not null);
or
select * from emp e where empno not in (select mgr from emp where e.empno=mgr);

24.Display the names of employees who are not working as SALESMAN or CLERK or ANALYST
select job from emp where job not in (‘CLERK’,’ANALYST’,’SALESMAN’);

25.Display all rows from emp table. The system should wait after every screen full of information
set pause on;

26.Display the total number of employees working in the company
select count(*) from emp;

27.Display the total salary and total commission to all employees
select sum(sal), sum(nvl(comm,0)) from emp;

28.Display the maximum salary from emp table
select max(sal) from emp;

29.Display the minimum salary from emp table
select min(sal) from emp;

30.Display the average salary from emp table
select avg(sal) from emp;

31.Display the maximum salary being paid to CLERK
select max(sal) from emp where job=’CLERK’;

32.Display the maximum salary being paid in dept no 20
select max(sal) from emp where deptno=20;

33.Display the minimum salary being paid to any SALESMAN
select min(sal) from emp where job=’SALESMAN’;

34.Display the average salary drawn by managers
select avg(sal) from emp where job=’MANAGER’;

35.Display the total salary drawn by analyst working in dept no 40
select sum(sal)+sum(nvl(comm,0)) from emp where deptno=40;

36.Display the names of employees in order of salary i.e. the name of the employee earning lowest salary shoud appear first
select ename from emp order by sal;

37.Display the names of employees in descending order of salary
select ename from emp order by sal desc;

38.Display the details from emp table in order of emp name
select ename from emp order by ename;

39.Display empnno,ename,deptno and sal. Sort the output first based on name and within name by deptno and witdhin deptno by sal;
select * from emp order by ename,deptno,sal;

40) Display the name of employees along with their annual salary(sal*12).
the name of the employee earning highest annual salary should appear first?
Ans:select ename,sal,sal*12 “Annual Salary” from emp order by “Annual Salary” desc;

41) Display name,salary,Hra,pf,da,TotalSalary for each employee.
The out put should be in the order of total salary ,hra 15% of salary ,DA 10% of salary .pf 5% salary Total Salary
will be (salary+hra+da)-pf?
Ans: select ename,sal SA,sal*0.15 HRA,sal*0.10 DA,sal*5/100 PF, sal+(sal*0.15)+(sal*0.10)-(sal*.05) TOTALSALARY
from emp ORDER BY TOTALSALARY DESC;

42) Display Department numbers and total number of employees working in each Department?
Ans: select deptno,count(*) from tvsemp group by deptno;

43) Display the various jobs and total number of employees working in each job group?
Ans: select job,count(*) from tvsemp group by job;

44)Display department numbers and Total Salary for each Department?
Ans: select deptno,sum(sal) from tvsemp group by deptno;

45)Display department numbers and Maximum Salary from each Department?
Ans: select deptno,max(Sal) from tvsemp group by deptno;

46)Display various jobs and Total Salary for each job?
Ans: select job,sum(sal) from tvsemp group by job;

47)Display each job along with min of salary being paid in each job group?
Ans: select job ,min(sal) from tvsemp group by job;

48) Display the department Number with more than three employees in each department?
Ans: select deptno ,count(*) from tvsemp group by deptno having count(*)>3;

49) Display various jobs along with total salary for each of the job where total salary is greater than 40000?
Ans: select job,sum(sal) from tvsemp group by job having sum(SAl)>40000;

50) Display the various jobs along with total number of employees in each job.The
output should contain only those jobs with more than three employees?
Ans: select job,count(*) from tvsemp group by job having count(*)>3;

51) Display the name of employees who earn Highest Salary?
Ans: select ename, sal from tvsemp where sal>=(select max(sal) from tvsemp );

52) Display the employee Number and name for employee working as clerk and earning highest salary among the clerks?
Ans: select ename,empno from tvsemp where sal=(select max(sal) from tvsemp where job=’CLERK’) and job=’CLERK’ ;

53) Display the names of salesman who earns a salary more than the Highest Salary of the clerk?
Ans: select ename,sal from tvsemp where sal>(select max(sal) from tvsemp where job=’CLERK’) AND job=’SALESMAN’;

54) Display the names of clerks who earn a salary more than the lowest Salary of any salesman?
Ans: select ename,sal from tvsemp where sal>(select min(sal) from tvsemp where job=’SALESMAN’) and job=’CLERK’;

55) Display the names of employees who earn a salary more than that of jones or that of salary greater than that of scott?
Ans: select ename,sal from tvsemp where sal>all(select sal from tvsemp where ename=’JONES’ OR ename=’SCOTT’);

56) Display the names of employees who earn Highest salary in their respective departments?
Ans: select ename,sal,deptno from tvsemp where sal in (select max(sal) from tvsemp group by deptno);

57) Display the names of employees who earn Highest salaries in their respective job Groups?
Ans: select ename,job from tvsemp where sal in (select max(sal) from tvsemp group by job);

58) Display employee names who are working in Accounting department?
Ans: select e.ename,d.dname from emp e,dept d where e.deptno=d.deptno and d.dname=’ACCOUNTING’;

59) Display the employee names who are Working in Chicago?
Ans: select e.ename,d.loc from emp e,tvsdept d where e.deptno=d.deptno and d.loc=’CHICAGO’;

60) Display the job groups having Total Salary greater than the maximum salary for Managers?
Ans: select job ,sum(sal) from tvsemp group by job having sum(sal) >(select max(sal) from tvsemp where job=’MANAGER’);

61) Display the names of employees from department number 10 with salary greater than that of ANY employee working in other departments?
Ans: select ename,deptno from tvsemp where sal>any(select min(sal) from tvsemp where deptno!=10 group by deptno) and deptno=10 ;

62) Display the names of employees from department number 10 with salary greater than that of ALL employee working in other departments?
Ans: select ename,deptno from tvsemp where sal>all(select max(sal) from tvsemp where deptno!=10 group by deptno) and deptno=10 ;

63) Display the names of mployees in Upper Case?
Ans: select upper(ename) from tvsemp;

64) Display the names of employees in Lower Case?
Ans: select Lower(ename) from tvsemp;

65) Display the names of employees in Proper case?
Ans: select InitCap(ename)from tvsemp;

Q:66) Find the length of your name using Appropriate Function?
Ans: select lentgh(‘RAMA’) from dual;

67) Display the length of all the employee names?
Ans: select length(ename) from tvsemp;

68) Display the name of employee Concatinate with Employee Number?
Ans: select ename||’ ‘||empno from tvsemp;

69) Use appropriate function and extract 3 characters starting from 2 characters from the following string ‘Oracle’ i.e., the out put should be ac?
Ans: select substr(‘Oracle’,3,2) from dual;

70) Find the first occurance of character a from the following string Computer Maintenance Corporation?
Ans: select lstr(‘Computer Maintenance Corporation’,’a’ ) from dual;

71) Replace every occurance of alphabet A with B in the string .Alliens (Use Translate function)?
Ans: select translate(‘Alliens’,’A’,’B’) from Dual;

72) Display the information from the employee table . where ever job Manager is found it should be displayed as Boss?
Ans: select ename ,replace(job,’MANAGER’,’BOSS’) from tvsemp;

73) Display empno,ename,deptno from tvsemp table. Instead of display department numbers
display the related department name(Use decode function)?
Ans: select empno,ename,deptno,Decode(deptno,10,’ACCOUNTING’
,20,’RESEARCH’,30,’SALES’,’OPERATIONS’)DName from tvsemp;

74) Display your Age in Days?
Ans: select sysdate-to_date(’30-jul-1977′) from dual;

75) Display your Age in Months?
Ans: select months_between(sysdate,to_date(’30-jul-1977′)) from dual;

76) Display current date as 15th August Friday Nineteen Nienty Seven?
Ans: select To_char(sysdate,’ddth Month Day year’) from dual;

77) Display the following output for each row from tvsemp table?
Ans: Q:78

78) Scott has joined the company on 13th August ninteen ninety?
Ans: select empno,ename,to_char(Hiredate,’Day ddth Month year’) from tvsemp;

79) Find the nearest Saturday after Current date?
Ans: select next_day(sysdate,’Saturday’) from dual;

80) Display the current time?
Ans: select To_Char(sysdate,’HH:MI:SS’) from dual;

81) Display the date three months before the Current date?
Ans: select Add_months(sysdate,-3) from dual

82) Display the common jobs from department number 10 and 20?
Ans: select job from tvsemp where job in (select job from tvsemp where deptno=20) and deptno=10;

83) Display the jobs found in department 10 and 20 Eliminate duplicate jobs?
Ans: select Distinct job from tvsemp where deptno in(10,20);

84) Display the jobs which are unique to department 10?
Ans: select job from tvsemp where deptno=10;

85) Display the details of those employees who do not have any person working under him?
Ans: select empno,ename,job from tvsemp where empno not in (select mgr from tvsemp where mgr is not null );

86) Display the details of those employees who are in sales department and grade is 3?
Ans: select e.ename,d.dname,grade from emp e,dept d ,salgrade where e.deptno=d.deptno and dname=’SALES’ and grade=3;

87) Display thoes who are not managers?
Ans: select ename from tvsemp where job!=’MANAGER’;

88) Display those employees whose name contains not less than 4 characters?
Ans: select ename from tvsemp where length(ename)>=4

89) Display those department whose name start with”S” while location name ends with “K”?
Ans: select e.ename,d.loc from tvsemp e ,tvsdept d where d.loc like(‘%K’) and ename like(‘S%’)

90) Display those employees whose manager name is Jones?
Ans: select e.ename Superior,e1.ename Subordinate from tvsemp e,e1 where e.empno=e1.mgr and e.ename=’JONES’;

91) Display those employees whose salary is more than 3000 after giving 20% increment?
Ans: select ename,sal,(sal+(sal*0.20)) from tvsemp where (sal+(sal*0.20))>3000;

92) Display all employees with their department names?
Ans: select e.ename,d.dname from tvsemp e, tvsdept d where e.deptno=d.deptno

93) Display ename who are working in sales department?
Ans: select e.ename,d.dname from emp e,dept d where e.deptno=d.deptno and d.dname=’SALES’;

94) Display employee name,dept name,salary,and commission for those sal in between 2000
to 5000 while location is Chicago?
Ans: Select e.ename,d.dname,e.sal,e.comm from tvsemp e,dept d where e.deptno=d.deptno and sal between 2000 and 5000;

95) Display those employees whose salary is greater than his managers salary?
Ans: Select e.ename,e.sal,e1.ename,e1.sal from tvsemp e,e1 where e.mgr=e1.empno and e.sal>e1.sal;

96) Display those employees who are working in the same dept where his manager is work?
Ans: select e.ename,e.deptno,e1.ename,e1.deptno from tvsemp e,e1 where e.mgr=e1.empno and e.deptno=e1.deptno;

97) Display those employees who are not working under any Manager?
Ans: select ename from tvsemp where mgr is null;

98) Display the grade and employees name for the deptno 10 or 30 but grade is not 4 while
joined the company before 31-DEC-82?
Ans: select ename,grade,deptno,sal from tvsemp ,salgrade where ( grade,sal) in
( select grade,sal from salgrade,tvsemp where sal between losal and hisal)
and grade!=4 and deptno in (10,30) and hiredate<’31-Dec-82

99) Update the salary of each employee by 10% increment who are not eligible for commission?
Ans: update tvsemp set sal= (sal+(sal*0.10)) where comm is null;

100) Delete those employees who joined the company before 31-Dec-82 while their department Location is New York or Chicago?
Ans: select e.ename,e.hiredate,d.loc from tvsemp e,tvsdept d where
e.deptno=d.deptno and hiredate<’31-Dec-82′ and d.loc in(‘NEW YORK’,’CHICAGO’);

Sql Queries2

101) Display employee name ,job,deptname,loc for all who are working as manager?

Ans: select e.ename,e.job,d.dname,d.loc from tvsemp e,tvsdept d where e.deptno=d.deptno

and e.empno in (select mgr from tvsemp where mgr is not null);102) Display those employees whose manager name is jones and also display their manager

name?

Ans: select e.ename sub,e1.ename from tvsemp e,e1 where e.mgr=e1.empno and e1.ename=’JONES’;

103) Display name and salary of ford if his salary is equal to hisal of his grade?

Ans: select ename,grade,hisal,sal from emp,salgrade where ename=’FORD’ and sal=hisal;

select grade,sal,hisal from tvsemp,salgrade where ename=’FORD’ and sal between losal and hisal;

select ename,sal,hisal,grade from tvsemp,salgrade where ename=’FORD’

and (grade,sal) in (select grade,hisal from salgrade,tvsemp where

sal between losal and hisal);

104) Display employee name ,job,deptname,his manager name ,his grade and make an

under department wise?

Ans: select e.ename sub,e1.ename sup,e.job,d.dname ,grade from tvsemp e,e1,salgrade,tvsdept d where e.mgr=e1.empno and e.sal between losal and hisal and e.deptno=d.deptno group by d.deptno,e.ename,e1.ename,e.job,d.dname,grade;

select e.ename sub,e1.ename sup,e.job,d.dname ,grade from tvsemp e,e1,salgrade,tvsdept d where e.mgr=e1.empno and e.sal between losal and hisal and e.deptno=d.deptno

105) List out all the employee names ,job,salary,grade and deptname for every one in a company except ‘CLERK’ . Sort on salary display the highest salary?

Ans: select e.ename ,e.job,e.sal,d.dname ,grade from tvsemp e,salgrade,tvsdept d where (e.deptno=d.deptno and e.sal between losal and hisal ) order by e.sal desc

106) Display employee name,job abd his manager .Display also employees who are with out

managers?

Ans: select e.ename ,e1.ename,e.job,e.sal,d.dname from tvsemp e,e1,tvsdept d where e.mgr=e1.empno(+) and e.deptno=d.deptno107) Display Top 5 employee of a Company?

Ans:

108) Display the names of those employees who are getting the highest salary?

Ans: select ename,sal from tvsemp where sal in (select max(sal) from tvsemp)

109) Display those employees whose salary is equal to average of maximum and minimum?

Ans: select * from tvsemp

where sal=(select (max(sal)+min(sal))/2 from tvsemp)

110) Select count of employees in each department where count >3?

Ans: select count(*) from tvsemp group by deptno having count(*)>3

111) Display dname where atleast three are working and display only deptname?

Ans: select d.dname from tvsdept d, tvsemp e where e.deptno=d.deptno group by d.dname having count(*)>3;

112) Display name of those managers name whose salary is more than average salary of

Company?

Ans: select distinct e1.ename,e1.sal from tvsemp e,e1,dept d where e.deptno=d.deptno and e.mgr=e1.empno and e1.sal> (select avg(sal) from tvsemp);

113) Display those managers name whose salary is more than average salary salary of his

employees?

Ans: select distinct e1.ename,e1.sal from tvsemp e,e1,dept d where e.deptno=d.deptno and e.mgr=e1.empno and e1.sal>any (select avg(sal) from tvsemp group by deptno);

114) Display employee name,sal,comm and netpay for those employees whose netpay is

greater than or equal to any other employee salary of the company?

Ans: select ename,sal,NVL(comm,0),sal+NVL(comm,0) from tvsemp where

sal+NVL(comm,0) >any (select e.sal from tvsemp e );

115) Display those employees whose salary is less than his manager but more than salary of

other managers?

Ans: select e.ename sub,e.sal from tvsemp e,e1,tvsdept d where

e.deptno=d.deptno and e.mgr=e1.empno

and e.sal<e1.sal

and e.sal >any (select e2.sal from tvsemp e2, e,tvsdept d1 where

e.mgr=e2.empno and d1.deptno=e.deptno);

116) Display all employees names with total sal of company with each employee name?

Ans:

117) Find the last 5(least) employees of company?

Ans:

118) Find out the number of employees whose salary is greater than their managers salary?

Ans: select e.ename,e.sal,e1.ename,e1.sal from tvsemp e,e1,tvsdept d where e.deptno=d.deptno and e.mgr=e1.empno and e.sal>e1.sal

119) Display the manager who are not working under president but they are working under

any other manager?

Ans: select e2.ename from emp e1,emp e2,emp e3 where e1.mgr=e2.empno and e2.mgr=e3.empno and e3.job!=’PRESIDENT’;

120) Delete those department where no employee working?

Ans: delete from tvsemp where empno is null;

121) Delete those records from emp table whose deptno not available in dept table?

Ans: delete from tvsemp e where e.deptno not in (select deptno from tvsdept)

122) Display those enames whose salary is out of grade available in salgrade table?

Ans: select empno,sal from tvsemp where sal<(select min(LOSAL) from salgrade )

OR sal>(select max(hisal) from salgrade)

123) Display employee name,sal,comm and whose netpay is greater than any othere in the

company?

Ans: select ename,sal,comm,sal+comm from tvsemp where sal+comm>any

(select sal+comm from tvsemp )

124) Display name of those employees who are going to retire 31-Dec-99 if maximum job period

is 30 years?

Ans: select empno, hiredate,sysdate, to_char(sysdate,’yyyy’) – to_char(hiredate,’yyyy’)

from tvsemp where to_char(sysdate,’yyyy’) – to_char(hiredate,’yyyy’)=30

125) Display those employees whose salary is odd value?

Ans: select ename ,sal from tvsemp where mod(sal,2)!=0

126) Display those employees whose salary contains atleast 3 digits?

Ans: select ename,sal from tvsemp where length(sal)=3

127) Display those employees who joined in the company in the month of Dec?

Ans: Select empno,ename from tvsemp where trim(to_char(hiredate,’Mon’))=trim(‘DEC’)

128) Display those employees whose name contains A?

Ans: select ename from tvsemp where ename like(‘%A%’)

129) Display those employees whose deptno is available in salary?

Ans: select ename,sal from tvsemp where deptno in (select distinct sal from tvsemp);

130) Display those employees whose first 2 characters from hiredate – last 2 characters sal?

Ans: select empno,hiredate,sal from tvsemp where trim(substr(hiredate,1,2))=trim(substr(sal,-2,2));

select hiredate,sal from tvsemp where to_Char(hiredate,’dd’)=trim(substr(sal,-2,2))

131) Display those employeess whose 10% of salary is equal to the year joining?

Ans: select ename ,sal,0.10*sal from tvsemp where 0.10*sal=trim(to_char(hiredate,’yy’))

132) Display those employees who are working in sales or research?

Ans: select e.ename from tvsemp e ,tvsdept d where e.deptno=d.deptno and d.dname in(‘SALES’,’RESEARCH’);

133) Display the grade of jones?

Ans: select ename,grade from tvsemp,salgrade where ( grade,sal) =

(select grade,sal from salgrade,tvsemp where sal between losal and hisal and ename=’JONES’)

134) Display those employees who joined the company before 15th of the month?

Ans: select ename ,hiredate from tvsemp where hiredate<’15-Jul-02′ and hiredate >=’01-jul-02′;

135) Display those employees who has joined before 15th of the month?

Ans: select ename ,hiredate from tvsemp where hiredate<’15-Jul-02′

136) Delete those records where no of employees in particular department is less than 3?

Ans: delete from tvsemp where deptno in (select deptno from tvsemp group by deptno having count(*) ❤

137A) Delete those employeewho joined the company 10 years back from today?

Ans: delete from tvsemp where empno in (select empno from tvsemp

where to_char(sysdate,’yyyy’)- to_char(hiredate,’yyyy’)>=10)

137B) Display the deptname the number of characters of which is equal to no of employee

in any other department?

Ans:

138) Display the deptname where no employee is working?

Ans: select deptno from tvsemp where empno is null;

139) Display those employees who are working as manager?

Ans: select e2.ename from tvsemp e1,e2 where e1.mgr=e2.empno and e2.empno is not null

140) Count th number of employees who are working as managers (Using set opetrator)?

Ans: select d.dname from tvsdept d where length(d.dname) in (select count(*) from tvsemp e where e.deptno!=d.deptno group by e.deptno)

141) Display the name of the dept those employees who joined the company on the same date?

Ans: select a.ename,b.ename from tvsemp a,tvsemp b where a.hiredate=b.hiredate and a.empno!=b.empno

142) Display those employees whose grade is equal to any number of sal but not equal to first number of sal?

Ans: select ename,sal,grade ,substr(sal,grade,1) from tvsemp,salgrade where

grade!=substr(sal,1,1) and grade = substr(sal,grade,1)

and sal between losal and hisal

143) Count the no of employees working as manager using set operation?

Ans: Select count(empno) from tvsemp where

empno in (select a.empno from tvsemp a

intersect

select b.mgr from tvsemp b)

144) Display the name of employees who joined the company on the same date?

Ans: select a.ename,b.ename from tvsemp a,tvsemp b where a.hiredate=b.hiredate and a.empno!=b.empno;

145) Display the manager who is having maximum number of employees working under him?

Ans: select e2.ename,count(*) from tvsemp e1,e2 where e1.mgr=e2.empno group by e2.ename Having count(*)=(select max(count(*)) from tvsemp e1,e2 where e1.mgr=e2.empno group by e2.ename)

146) List out the employee name and salary increased by 15% and express as whole number of Dollars?

Ans: select ename,sal,lpad(translate(sal,sal,((sal +(sal*0.15))/50)),5,’$’) from tvsemp

147) Produce the output of the emptable “EMPLOYEE_AND JOB” for ename and job ?

Ans: select ename”EMPLOYEE_AND”,job”JOB” FROM TVSEMP;

148) Lust of employees with hiredate in the format of ‘June 4 1988’?

Ans: select ename,to_char(hiredate,’Month dd yyyy’) from tvsemp;

149) print list of employees displaying ‘Just salary’ if more than 1500 if exactly 1500

display ‘on taget’ if less than 1500 display below 1500?

Ans: select ename,sal,

(

case when sal < 1500 then

‘Below_Target’

when sal=1500 then

‘On_Target’

when sal > 1500 then

‘Above_Target’

else

‘kkkkk’

end

)

from tvsemp

150) Which query to calculate the length of time any employee has been with the company

Ans: select hiredate,to_char(hiredate,’ HH:MI:SS’) FROM tvsemp

151) Given a string of the format ‘nn/nn’ . Verify that the first and last 2 characters are numbers .And that the middle character is ‘/’ Print the expressions ‘Yes’ IF valid

‘NO’ of not valid . Use the following values to test your solution’12/54′,01/1a,’99/98′?

Ans:

152) Employes hire on OR Before 15th of any month are paid on the last friday of that month

those hired after 15th are paid the last friday of th following month .print a list of employees .their hiredate and first pay date sort those who se salary contains first

digit of their deptno?

Ans: select ename,hiredate, LAST_DAY ( next_day(hiredate,’Friday’)),

(

case when to_char(hiredate,’dd’) <=(’15’) then

LAST_DAY ( next_day(hiredate,’Friday’))

when to_char(hiredate,’dd’)>(’15’) then

LAST_DAY( next_day(add_months(hiredate,1),’Friday’))

end

)

from tvsemp

153) Display those managers who are getting less than his employees salary?

Ans: select a.empno,a.ename ,a.sal,b.sal,b.empno,b.ename from tvsemp a, tvsemp b where a.mgr=b.empno and a.sal>b.sal

154) Print the details of employees who are subordinates to BLAKE?

Ans: select a.empno,a.ename ,b.ename from tvsemp a, tvsemp b where a.mgr=b.empno

and b.ename=’BLAKE’

151.Display those who working as manager using co related sub query

select * from emp where empno in (select mgr from emp);

152.Display those employees whose manager name is JONES and also with his manager name

select * from emp where mgr=(select empno from emp where ename=’JONES’) union select * from emp where empno =

(select mgr from emp where ename=’JONES’);

153.Define variable representing the expressions used to calculate on employees total annual renumaration

define emp_ann_sal=(sal+nvl(comm,0))*.12;

154.Use the variable in a statement which finds all employees who can earn 30000 a year or more

select * from emp where &emp_ann_sal>30000;

155.Find out how many managers are there with out listing them

select count(*) from emp where empno in (select mgr from emp);

156.Find out the avg sal and avg total remuneration for each job type remember salesman earn commission

select job,avg(sal+nvl(comm,0)),sum(sal+nvl(comm,0)) from emp group by job;

157.Check whether all employees number are indeed unique

select count(empno) ,count(distinct(empno)) from emp having count(empno)=(count(distinct(empno));

158.List out the lowest paid employees working for each manager, exclude any groups where minsal is less than

1000 sort the output by sal

select e.ename,e.mgr,e.sal from emp e where sal in (select min(sal) from emp where mgr=e.mgr) and

e.sal>1000 order by sal;

159.List ename,job,annual sal,depno,dname and grade who earn 30000 per year and who are not clerks

select e.ename,e.job,(e.sal+nvl(e.comm,0))*12,e.deptno,d.dname,s.grade from emp e,salgrade s,dept d

where e.sal between s.losal and s.hisal and e.deptno=d.deptno and (e.sal+nvl(comm,0))*12 > 30000

and e.job<>’CLERK’;

160.Find out th job that was falled in the first half of 1983 and the same job that was falled during the

same period on 1984

161.Find out the all employees who joined the company before their manager

select * from emp e where hiredate <(select hiredate from emp where empno=e.mgr);

162.List out the all employees by name and number along with their manager’s name and number also display

‘NO MANAGER’ who has no manager

select e.empno,e.ename,m.empno Manager,m.ename ManagerName from emp e,emp m where e.mgr=m.empno

union

select empno,ename,mgr,’NO Manager’ from emp where mgr is null;

163.Find out the employees who earned the highest sal in each job typed sort in descending sal order

select * from emp e where sal=(select max(sal) from emp where job=e.job);

164.Find out the employees who earned the min sal for their job in ascending order

select * from emp e where sal=(select min(sal) from emp where job=e.job) order by sal;

165.Find out the most recently hired employees in each dept order by hire date

select * from emp order by deptno,hiredate desc;

166.Display ename,sal and deptno for each employee who earn a sal greater than the avg of their department

order by deptno

select ename,sal,deptno from emp e where sal>(select avg(sal) from emp where deptno=e.deptno) order by deptno;

167.Display the department where there are no employees

select deptno,dname from dept where deptno not in (select distinct(deptno) from emp);

168.Display the dept no with highest annual remuneration bill as compensation

select deptno,sum(sal) from emp group by deptno having sum(sal)=(select max(sum(sal)) from emp group by deptno);

169.In which year did most people join the company. Display the year and number of employees

select count(*),to_char(hiredate,’yyyy’) from emp group by to_char(hiredate,’yyyy’);

170.Display avg sal figure for the dept

select deptno,avg(sal) from emp group by deptno;

171.Write a query of display against the row of the most recently hierd employee.display ename hire date

and column max date showing

select empno,hiredate from emp wher hiredate=(select max(hiredate) from emp);

172.Display employees who can earn more than lowest sal in dept no 30

select * from emp where sal > (select min(sal) from emp where deptno=30);

173.Find employees who can earn more than every employees in dept no 30

select * from emp where sal>(select max(sal) from emp where deptno=30);

select * from emp where sal>all(select sal from emp where deptno=30);

174.select dept name and deptno and sum of sal

break on deptno on dname;

select e.deptno,d.dname,sal from emp e,dept d where e.deptno=d.deptno order by e.deptno;

175.Find out avg sal and avg total remainders for each job type

176.Find all dept’s which have more than 3 employees

select deptno from emp group by deptno having count(*)>3;

177.If the pay day is next Friday after 15th and 30th of every month. What is the next pay day from

their hire date for employee in emp table

178.If an employee is taken by you today in your organization and is a policy in your company to have a

review after 9 months the joined date (and of 1st of next month after 9 months) how many days from today

your employee has to wait for a review

179.Display employee name and his sal whose sal is greater than highest avg of deptno

180.Display the 10 th record of emp table (without using rowid)

181.Display the half of the enames in upper case and remaining lower case

select concat(upper(substr(ename,0,length(ename)/2),lower(substr(ename,length(ename)/2+1,length(ename)))) from

emp;

182.Display the 10th record of emp table without using group by and rowid

183.Delete the 10th record of emp table

184.Create a copy of emp table

create table emp1 as select * from emp;

185.select ename if ename exists more than once

select distinct(ename) from emp e where ename in (select ename from emp where e.empno<>empno);

186.Display all enames in reverse order

select ename from emp order by ename desc;

187.Display those employee whose joining of month and grade is equal

select empno,ename from emp e,salgrade s where e.sal between s.losal and s.hisal and to_char(hiredate,

‘mm’)=grade;

188.Display those employee whose joining date is available in deptno

select * from emp where to_char(hiredate,’dd’) =deptno;

189.Display those employee name as follows A ALLEN, B BLAKE

select substr(ename,1,1)||”||ename from emp;

190.List out the employees ename,sal,pf from emp

select ename,sal,sal*15/100 pf from emp;

191.Display RSPS from emp without using updating,inserting

192.Create table emp with only one column empno

create table emp (empno number(5));

193.Add this column to emp table ename varchar2(20)

alter table emp add ename varchar2(20) not null;

194.OOPSI i forget to give the primary key constraint. Add it now

alter table emp add constraint emp_empno primary key (empno);

195.Now increase the length of ename column to 30 characters

alter table emp modify ename varchar2(30);

196.Add salary column to emp table

alter table emp add sal number(7,2);

197.I want to give a validation saying that sal can not be greater 10000(note give a name to this column)

alter table emp add constraint emp_sal_check check(sal<10000);

198.For the time being i have decided that i will not impose this validation. My boss has agreed to pay

more than 10000

alter table emp disable constraint emp_sal_check;

199.My boss has changed his mind. Now he doesn’t want to pay more than 10000 So revoke that salary constraint

alter table emp enable constraint emp_sal_check;

200.Add column called as mgr to your emp table

alter table emp add mgr number(5);

Sql Queries3

Q:1) Display the name of employees along with their annual salary(sal*12).

the name of the employee earning highest annual salary should appear first?

Ans: select ename,sal,sal*12 “Annual Salary” from emp order by “Annual Salary” desc;Q:2)Display name,salary,Hra,pf,da,TotalSalary for each employee.

The out put should be in the order of total salary ,hra 15% of salary ,

DA 10% of salary .pf 5% salary Total Salary will be (salary+hra+da)-pf?

Ans: select ename,sal SA,sal*0.15 HRA,sal*0.10 DA,sal*5/100 PF,

sal+(sal*0.15)+(sal*0.10)-(sal*.05) TOTALSALARY from emp ORDER BY TOTALSALARY DESC;

Q:3) Display Department numbers and total number of employees working in each Department?

Ans: select deptno,count(*) from emp group by deptno;

Q:4) Display the various jobs and total number of employees working in each job group?

Ans: select job,count(*) from emp group by job;

Q:5) Display department numbers and Total Salary for each Department?

Ans: select deptno,sum(sal) from emp group by deptno;

Q:6) Display department numbers and Maximum Salary from each Department?

Ans: select deptno,max(sal) from emp group by deptno;

Q:7) Display various jobs and Total Salary for each job?

Ans: select job,sum(sal) from emp group by job;

Q:8) Display each job along with min of salary being paid in each job group?

Ans: select job ,min(sal) from emp group by job;

Q:9) Display the department Number with more than three employees in each department?

Ans: select deptno ,count(*) from emp group by deptno having count(*)>3;

Q:10) Display various jobs along with total salary for each of the job

where total salary is greater than 40000?

Ans: select job,sum(sal) from emp group by job having sum(sal)>40000;

Q:11) Display the various jobs along with total number of employees in each job.The output should contain only those jobs with more than three employees?

Ans: select job,count(*) from emp group by job having count(*)>3;

Q:12) Display the name of employee who earn Highest Salary?

Ans: select ename, sal from emp where sal>=(select max(sal) from emp );

Q:13) Display the employee Number and name for employee working as clerk and earning highest salary among the clerks?

Ans: select ename,empno from emp where sal=(select max(sal) from emp where

job=’CLERK’) and job=’CLERK’ ;

Q:14) Display the names of salesman who earns a salary more than the Highest Salary of the Clerk?

Ans: select ename,sal from emp where sal>(select max(sal) from emp

where job=’CLERK’) AND job=’SALESMAN’;

Q:15) Display the names of clerks who earn a salary more than the lowest Salary of any Salesman?

Ans: select ename,sal from emp where sal>(select min(sal) from emp where job=’SALESMAN’) and job=’CLERK’;

Q:16) Display the names of employees who earn a salary more than that of jones or that of salary greater than that of scott?

Ans: select ename,sal from emp where sal>all(select sal from emp where

ename=’JONES’ OR ename=’SCOTT’);

Q:17) Display the names of employees who earn Highest salary in their respective departments?

Ans: select ename,sal,deptno from emp where sal in (select max(sal) from emp group by deptno);

Q:18) Display the names of employees who earn Highest salaries in their respective job Groups?

Ans: select ename,job from emp where sal in (select max(sal) from emp group by job);

Q:19) Display employee names who are working in Accounting department?

Ans: select e.ename,d.dname from emp e,dept d where e.deptno=d.deptno and d.dname=’ACCOUNTING’;

Q:20) Display the employee names who are Working in Chicago?

Ans: select e.ename,d.loc from emp e,dept d where e.deptno=d.deptno and d.loc=’CHICAGO’;

Q:21) Display the job groups having Total Salary greater than the maximum salary for Managers?

Ans: select job ,sum(sal) from emp group by job having sum(sal) >(select max(sal) from emp where job=’MANAGER’);

Q:22) Display the names of employees from department number 10 with salary greater than that of ANY employee working in other departments?

Ans: select ename,deptno from emp where sal>any(select min(sal) from emp where deptno!=10 group by deptno) and deptno=10 ;

Q:23) Display the names of employees from department number 10 with salary greater than that of ALL employee working in other departments?

Ans: select ename,deptno from emp where sal>all(select max(sal) from emp where deptno!=10 group by deptno) and deptno=10 ;

Q:24) Display the names of employees in Upper Case?

Ans: select upper(ename) from emp;

Q:25) Display the names of employees in Lower Case?

Ans: select Lower(ename) from emp;

Q:26) Display the names of employees in Proper case?

Ans: select InitCap(ename)from emp;

Q:27) Find the length of your name using Appropriate Function?

Ans: select lentgh(‘SRINIVASARAO’) from dual;

Q:28) Display the length of all the employee names?

Ans: select length(ename) from emp;

Q:29) Display the name of employee Concatinate with Employee Number?

Ans: select ename||’ ‘||empno from emp;

Q:30) Use appropriate function and extract 3 characters starting from 2 characters from the following string ‘Oracle’ i.e., the out put should be ac?

Ans: select substr(‘Oracle’,3,2) from dual;

Q:31) Find the first occurance of character a from the following string Computer Maintenance Corporation?

Ans: select lstr(‘Computer Maintenance Corporation’,’a’ ) from dual;

Q:32) Replace every occurance of alphabet A with B in the string .Alliens (Use Translate function)?

Ans: select translate(‘Alliens’,’A’,’B’) from Dual;

Q:33) Display the information from the employee table . where ever job Manager is found it should be displayed as Boss?

Ans: select ename ,replace(job,’MANAGER’,’BOSS’) from emp;

Q:34) Display empno,ename,deptno from emp table. Instead of display department numbers display the related department name(Use decode function)?

Ans: select empno,ename,deptno,Decode(deptno,10,’ACCOUNTING’

,20,’RESEARCH’,30,’SALES’,’OPERATIONS’)DName from emp;

Q:35) Display your Age in Days?

Ans: select sysdate-to_date(’30-jul-1977′) from dual;

Q:36) Display your Age in Months?

Ans: select months_between(sysdate,to_date(’30-jul-1977′)) from dual;

Q:37) Display current date as 15th August Friday Nineteen Nienty Seven?

Ans: select To_char(sysdate,’ddth Month Day year’) from dual;

Q:38) Display the following output for each row from emp table?

Ans: Q:39

Q:39) Scott has joined the company on 13th August ninteen ninety?

Ans: select empno,ename,to_char(Hiredate,’Day ddth Month year’) from emp;

Q:40) Find the nearest Saturday after Current date?

Ans: select next_day(sysdate,’Saturday’) from dual;

Q:41) Display the current time?

Ans: select To_Char(sysdate,’HH:MI:SS’) from dual;

Q:42) Display the date three months before the Current date?

Ans: select Add_months(sysdate,-3) from dual;

Q:43) Display the common jobs from department number 10 and 20?

Ans: select job from emp where job in (select job from emp where deptno=20) and deptno=10;

Q:44) Display the jobs found in department 10 and 20 Eliminate duplicate jobs?

Ans: select Distinct job from emp where deptno in(10,20);

Q:45) Display the jobs which are unique to department 10?

Ans: select job from emp where deptno=10;

Q:46) Display the details of those employees who do not have any person working under him?

Ans: select empno,ename,job from emp where empno not in (select mgr from emp where mgr is not null );

Q:47)Display the details of those employees who are in sales department and grade is 3?

Ans: select e.ename,d.dname,grade from emp e,dept d ,salgrade where e.deptno=d.deptno and dname=’SALES’ and grade=3;

Q:48) Display those who are not managers?

Ans: select ename from emp where job!=’MANAGER’;

Q:49) Display those employees whose name contains not less than 4 characters?

Ans: select ename from emp where length(ename)>=4;

Q:50) Display those department whose name start with”S” while location name ends with “K”?

Ans: select e.ename,d.loc from emp e ,dept d where d.loc like(‘%K’) and ename like(‘S%’);

Q:51) Display those employees whose manager name is Jones?

Ans: select e.ename Superior,e1.ename Subordinate from emp e,e1 where e.empno=e1.mgr and e.ename=’JONES’;

Q:52) Display those employees whose salary is more than 3000 after giving 20% increment?

Ans: select ename,sal,(sal+(sal*0.20)) from emp where (sal+(sal*0.20))>3000;

Q:53) Display all employees with their department names?

Ans: select e.ename,d.dname from emp e, dept d where e.deptno=d.deptno;

Q:54) Display ename who are working in sales department?

Ans: select e.ename,d.dname from emp e,dept d where e.deptno=d.deptno and d.dname=’SALES’;

Q:56) Display employee name,dept name,salary,and commission for those sal in between 2000 to 5000 while location is Chicago?

Ans: Select e.ename,d.dname,e.sal,e.comm from emp e,dept d where e.deptno=d.deptno and sal between 2000 and 5000;

Q:57) Display those employees whose salary is greater than his managers salary?

Ans: Select e.ename,e.sal,e1.ename,e1.sal from emp e,e1 where e.mgr=e1.empno and e.sal>e1.sal;

Q:58) Display those employees who are working in the same dept where his manager is work?

Ans: select e.ename,e.deptno,e1.ename,e1.deptno from emp e,e1 where e.mgr=e1.empno and e.deptno=e1.deptno;

Q:59) Display those employees who are not working under any Manager?

Ans: select ename from emp where mgr is null;

Q:60) Display the grade and employees name for the deptno 10 or 30 but grade is not 4 while joined the company before 31-DEC-82?

Ans: select ename,grade,deptno,sal from emp ,salgrade where ( grade,sal) in

( select grade,sal from salgrade,emp where sal between losal and hisal)

and grade!=4 and deptno in (10,30) and hiredate<’31-Dec-82′;

Q:61) Update the salary of each employee by 10% increment who are not eligible for commission?

Ans: update emp set sal= (sal+(sal*0.10)) where comm is null;

Q:62) Delete those employees who joined the company before 31-Dec-82 while their department Location is New York or Chicago?

Ans: select e.ename,e.hiredate,d.loc from emp e,dept d where

e.deptno=d.deptno and hiredate<’31-Dec-82′ and d.loc in(‘NEW YORK’,’CHICAGO’);

Q:63) Display employee name ,job,deptname,loc for all who are working as manager?

Ans: select e.ename,e.job,d.dname,d.loc from emp e,dept d where e.deptno=d.deptno

and e.empno in (select mgr from emp where mgr is not null);

Q:64) Display those employees whose manager name is jones and also display their manager name?

Ans: select e.ename sub,e1.ename from emp e,e1 where e.mgr=e1.empno and e1.ename=’JONES’;

Q:65) Display name and salary of ford if his salary is equal to hisal of his grade?

Ans: select ename,grade,hisal,sal from emp,salgrade where ename=’FORD’ and sal=hisal;

select grade,sal,hisal from emp,salgrade where ename=’FORD’ and sal between losal and hisal;

select ename,sal,hisal,grade from emp,salgrade where ename=’FORD’

and (grade,sal) in (select grade,hisal from salgrade,emp where

sal between losal and hisal);

Q66) Display employee name ,job,deptname,his manager name ,his grade and make an under department wise?

Ans: select e.ename sub,e1.ename sup,e.job,d.dname ,grade from emp e,e1,salgrade,dept d where e.mgr=e1.empno and e.sal between losal and hisal and e.deptno=d.deptno group by d.deptno,e.ename,e1.ename,e.job,d.dname,grade;

select e.ename sub,e1.ename sup,e.job,d.dname ,grade from emp e,e1,salgrade,tvsdept d where e.mgr=e1.empno and e.sal between losal and hisal and e.deptno=d.deptno;

Q:67) List out all the employee names ,job,salary,grade and deptname for every one in a company except ‘CLERK’ . Sort on salary display the highest salary?

Ans: select e.ename ,e.job,e.sal,d.dname ,grade from emp e,salgrade,dept d where (e.deptno=d.deptno and e.sal between losal and hisal ) order by e.sal desc;

Q:68) Display employee name,job abd his manager .Display also employees who are with out managers?

Ans: select e.ename ,e1.ename,e.job,e.sal,d.dname from emp e,e1,dept d where e.mgr=e1.empno(+) and e.deptno=d.deptno;

Q:69) Display Top 5 employee of a Company?

Ans:

Q:70) Display the names of those employees who are getting the highest salary?

Ans: select ename,sal from emp where sal in (select max(sal) from emp);

Q:71) Display those employees whose salary is equal to average of maximum and minimum?

Ans: select * from emp

where sal=(select (max(sal)+min(sal))/2 from emp);

Q:72) Select count of employees in each department where count >3?

Ans: select count(*) from emp group by deptno having count(*)>3

Q:73) Display dname where atleast three are working and display only deptname?

Ans: select d.dname from dept d, emp e where e.deptno=d.deptno group by d.dname having count(*)>3;

Q:74) Display name of those managers name whose salary is more than average salary of Company?

Ans: select distinct e1.ename,e1.sal from emp e,e1,dept d where e.deptno=d.deptno and e.mgr=e1.empno and e1.sal> (select avg(sal) from emp);

Q:75) Display those managers name whose salary is more than average salary salary of his employees?

Ans: select distinct e1.ename,e1.sal from emp e,e1,dept d where e.deptno=d.deptno and e.mgr=e1.empno and e1.sal>any (select avg(sal) from emp group by deptno);

Q:76) Display employee name,sal,comm and netpay for those employees whose netpay is greater than or equal to any other employee salary of the company?

Ans: select ename,sal,NVL(comm,0),sal+NVL(comm,0) from emp where

sal+NVL(comm,0) >any (select e.sal from emp e );

Q:77) Display those employees whose salary is less than his manager but more than salary of other managers?

Ans: select e.ename sub,e.sal from emp e,e1,dept d where

e.deptno=d.deptno and e.mgr=e1.empno

and e.sal<e1.sal

and e.sal >any (select e2.sal from emp e2, e,dept d1 where

e.mgr=e2.empno and d1.deptno=e.deptno);

Q:78) Display all employees names with total sal of company with each employee name?

Ans:

Q:79) Find the last 5(least) employees of company?

Ans:

Q:80) Find out the number of employees whose salary is greater than their managers salary?

Ans: select e.ename,e.sal,e1.ename,e1.sal from emp e,e1,dept d where e.deptno=d.deptno and e.mgr=e1.empno and e.sal>e1.sal;

Q:81) Display the manager who are not working under president but they are working under any other manager?

Ans: select e2.ename from emp e1,emp e2,emp e3 where e1.mgr=e2.empno and e2.mgr=e3.empno and e3.job!=’PRESIDENT’;

Q:82) Delete those department where no employee working?

Ans: delete from emp where empno is null;

Q:83) Delete those records from emp table whose deptno not available in dept table?

Ans: delete from emp e where e.deptno not in (select deptno from dept);

Q:84) Display those enames whose salary is out of grade available in salgrade table?

Ans: select empno,sal from emp where sal<(select min(LOSAL) from salgrade )

OR sal>(select max(hisal) from salgrade);

Q:85) Display employee name,sal,comm and whose netpay is greater than any other in the company?

Ans: select ename,sal,comm,sal+comm from emp where sal+comm>any

(select sal+comm from emp );

Q:86) Display name of those employees who are going to retire 31-Dec-99 if maximum job period is 30 years?

Ans: select empno, hiredate,sysdate, to_char(sysdate,’yyyy’) – to_char(hiredate,’yyyy’)

from emp where to_char(sysdate,’yyyy’) – to_char(hiredate,’yyyy’)=30;

Q:87) Display those employees whose salary is odd value?

Ans: select ename ,sal from emp where mod(sal,2)!=0;

Q:88) Display those employees whose salary contains atleast 3 digits?

Ans: select ename,sal from emp where length(sal)=3;

Q:89) Display those employees who joined in the company in the month of Dec?

Ans: Select empno,ename from emp where trim(to_char(hiredate,’Mon’))=trim(‘DEC’);

Q:90) Display those employees whose name contains A?

Ans: select ename from emp where ename like(‘%A%’);

Q:91) Display those employees whose deptno is available in salary?

Ans: select ename,sal from emp where deptno in (select distinct sal from emp);

Q:92) Display those employees whose first 2 characters from hiredate – last 2 characters sal?

Ans: select empno,hiredate,sal from emp where trim(substr(hiredate,1,2))=trim(substr(sal,-2,2));

select hiredate,sal from emp where to_Char(hiredate,’dd’)=trim(substr(sal,-2,2));

Q:93) Display those employeess whose 10% of salary is equal to the year joining?

Ans: select ename ,sal,0.10*sal from emp where 0.10*sal=trim(to_char(hiredate,’yy’));

Q:94) Display those employees who are working in sales or research?

Ans: select e.ename from emp e ,dept d where e.deptno=d.deptno and d.dname in(‘SALES’,’RESEARCH’);

Q:95) Display the grade of jones?

Ans: select ename,grade from emp,salgrade where ( grade,sal) =

(select grade,sal from salgrade,emp where sal between losal and hisal and ename=’JONES’);

Q:96) Display those employees who joined the company before 15th of the month?

Ans: select ename ,hiredate from emp where hiredate<’15-Jul-02′ and hiredate >=’01-jul-02′;

Q:97) Display those employees who has joined before 15th of the month?

Ans: select ename ,hiredate from emp where hiredate<’15-Jul-02′

Q:98) Delete those records where no of employees in particular department is less than 3?

Ans: delete from emp where deptno in (select deptno from emp group by deptno having count(*) ;

Q:99A) Delete those employeewho joined the company 10 years back from today?

Ans: delete from emp where empno in (select empno from emp

where to_char(sysdate,’yyyy’)- to_char(hiredate,’yyyy’)>=10);

Q:99B) Display the deptname the number of characters of which is equal to no of employee in any other department?

Ans:

Q:100) Display the deptname where no employee is working?

Ans: select deptno from emp where empno is null;

Most Common SQL Commands

SQL statements can be grouped in different categories:

Data Definition Language(DDL) Commands

CREATE: creates a new database object, such as a table.
ALTER: used to modify the database object
DROP: used to delete the objects.

Data Manipulation Language(DML) Commands

INSERT: used to insert a new data row record in a table.
UPDATE: used to modify an existing record in a table.
DELETE: used delete a record from the table.

Data Query Language(DQL) Commands

SELECT: it is the DQL command to select data from the database.

Data Control Language(DCL) Commands

GRANT: used to assign permission to users to access database objects.
REVOKE: used to deny permission to users to access database objects.

Data Transfer Language(DTL) Commands

COMMIT: used to save any transaction into the database permanently.
ROLLBACK: restores the database to the last committed state.

CREATE DATABASE

The first thing we need to do to work with SQL is to create a database. The CREATE DATABASE statement does exactly that.

Example:

CREATE DATABASE testDB

CREATE TABLE

The CREATE TABLE statement creates a new table in a database.

Example:

CREATE TABLE Employees (

EmployeeID int,

FirstName varchar(255),

LastName varchar(255),

Department varchar(255)

);

INSERT INTO

The INSERT INTO statement inserts new rows of data into a table

Example:

INSERT INTO Employees (FirstName, LastName, Department)

VALUES ('Sam', 'Burger', 'IT');

SELECT

SELECT is one of the main and most used SQL command. It selects data from a database and returns the table of results, called the result-set.

Example:

SELECT firstName, lastName

FROM Employees;

SELECT *

The SELECT command when used with an asterisk * operator, selects all records from a specified table.

Example:

SELECT * FROM Employees

SELECT DISTINCT

SELECT DISTINCT returns only the data that is distinct; i.e. does not include duplicate entries.

Example:

SELECT DISTINCT Department FROM Employees;

SELECT INTO

The SELECT INTO statement selects specified data from a table and copies it to another table.

Example:

SELECT firstName, entryGraduated INTO StudentAlumni

FROM Students;

SELECT TOP

SELECT TOP specifies the maximum number or percentage of data entries to return in a result-set.

SELECT TOP 50 PERCENT * FROM Customers;

WHERE

The WHERE clause is used to filter results based on a specified condition.

Example:

SELECT * FROM Employees

WHERE department = 'IT';

GROUP BY

The GROUP BY command arranges identical data from different rows into groups, thus creating summarizing rows.

Example:

SELECT COUNT(Department), Department

FROM Employees

GROUP BY Department;

HAVING

The HAVING clause performs the same as the WHERE clause, but the difference is that HAVING only works with aggregate functions. Likewise, WHERE clause doesn’t work with aggregate functions.

Example:

SELECT COUNT(Department), Department

FROM Employees

GROUP BY Department

HAVING COUNT(Department) > 2;

The IN operator includes multiple values into the WHERE clause.

Example:

SELECT * FROM Employees

WHERE Department IN ('IT', 'Graphics', 'Marketing');

BETWEEN

BETWEEN operator filters the results and returns only the ones that fit the specified range.

Example:

SELECT * FROM Employees

WHERE JoiningDate BETWEEN '01-01-2015' AND `01-01-2020`;

AND / OR

The AND and OR are conditional statements. In AND, all conditions must meet a specified criteria. In OR any of the conditions that satisfy a given criteria returns a result.

Example AND:

SELECT * FROM Employees

WHERE Department = 'IT' AND JoiningDate > '01-01-2015';

Example OR:

SELECT * FROM Employees

WHERE Department ='IT' OR Department = 'Graphics';

AS (Alias)

AS works as an alias. With AS, we can rename a column to something more meaningful or shorter in the query, without having to change the name in the database.

Example:

SELECT FirstName AS fname, LastName AS lname

FROM Employees;

INNER JOIN

INNER JOIN combines rows from different tables.

Example:

SELECT Orders.ID, Customers.Name

FROM Orders

INNER JOIN Customers ON Orders.ID = Customers.ID;

LEFT JOIN

LEFT JOIN retrieves records from the left table that match records in the right table.

Example:

SELECT Customers.CustomerName, Orders.OrderID

FROM Customers

LEFT JOIN Orders ON Customers.CustomerID = Orders.CustomerID

ORDER BY Customers.CustomerName;

RIGHT JOIN

Opposite of the LEFT JOIN, the RIGHT JOIN retrieves records from the right table that match records in the left table.

Example:

SELECT Orders.OrderID, Employees.LastName

FROM Orders

RIGHT JOIN Employees ON Orders.EmployeeID = Employees.EmployeeID

ORDER BY Orders.OrderID;

FULL JOIN

FULL JOIN returns all the records that match either in left or right tables.

Example:

SELECT Customers.Name, CustomerOrders.ID

FROM Customers

FULL OUTER JOIN Orders ON Customers.ID = CustomerOrders.customerID

ORDER BY Customers.Name;

DELETE

The DELETE statement removes certain rows from the table that meet a specified condition.

Example:

DELETE FROM Employees

WHERE FirstName = 'Sam' AND LastName = 'Burger';

ALTER TABLE

We use ALTER TABLE to add or remove columns from a table.

Example:

ALTER TABLE Employees

ADD JoiningDate date;

TRUNCATE TABLE

TRUNCATE TABLE removes data entries from a table in a database, but keeps the table structure.

Example:

TRUNCATE TABLE temp_table

DROP TABLE

DROP TABLE statement deletes the whole table with its column parameters and datatype settings.

Example:

DROP TABLE temp_table

DROP DATABASE

DROP DATABASE deletes the whole specified database together with all its parameters and data.

Be extra cautious when using this command.

Example:

DROP DATABASE temp_db

How to use the SQL Drop, Truncate and Delete Statements

The SQL DELETE statement is used to delete records from a table whereas the DROP statement is used to delete a table or a database.

The TRUNCATE TABLE statement can also be used to delete records from a table.

Deleting Records From a Table

The DELETE statement in SQL is used to delete records from a database table. We can remove all records from a table or delete specific records using the WHERE clause.

DELETE FROM table_name

WHERE condition;

SQL DELETE Statement Examples

Let’s assume we have a table called “Employees” with the following records:

+------------+-----------+----------+------------+

+------------+-----------+----------+------------+

| 2 | Jacob | Thornton | IT |

| 3 | Su | Bird | Marketing |

| 4 | Sam | Burger | IT |

+------------+-----------+----------+------------+

Delete a Single Record

The following code removes “Jacob Thornton” from the “Employees” table:

DELETE FROM Employees

WHERE FirstName = 'Jacob'

AND LastName = 'Thornton';

Note: In the above example, we use two conditions, WHERE and AND, i.e. by first name and last name. This is to ensure we delete the correct record, in case there is another employee with the same first name.

Delete All Records From a Table

The following code deletes all records from the “Employees” table:

DELETE * FROM Employees;

Note: The DELETE statement removes the records from a table, but does not delete the table itself.

SQL TRUNCATE TABLE Statement

The TRUNCATE TABLE statement can also be used to delete records from a table, but not the table instead.

Example:

TRUNCATE TABLE table_name;

SQL Drop Statement

The DROP statement in SQL is used to delete a table or a database.

How to Drop a Table in SQL

The following code drops a table called “Employees”:

DROP TABLE "Employees";

Note: Take extra care when using the DROP statement. When dropping a table, it will delete all records inside the table as well.

How to Drop a Database in SQL

The following code drops a database called “EmployeesDB”:

DROP DATABASE "EmployeesDB";

Note: Take extra care when using the DROP statement. When dropping a database, it will delete all tables inside the database.

SQL Queries Set 4

Q:1) Display the name of employees along with their annual salary(sal*12). the name of the employee earning highest annual salary should appear first?

Ans: select ename,sal,sal*12 “Annual Salary” from emp order by “Annual Salary” desc;Q:2)Display name,salary,Hra,pf,da,TotalSalary for each employee. The out put should be in the order of total salary ,hra 15% of salary , DA 10% of salary .pf 5% salary Total Salary will be (salary+hra+da)-pf?

Ans: select ename,sal SA,sal*0.15 HRA,sal*0.10 DA,sal*5/100 PF,sal+(sal*0.15)+(sal*0.10)-(sal*.05) TOTALSALARY from emp ORDER BY TOTALSALARY DESC;