Seo Services

Fast Instant Approval Directory Submission Site

2013-04-06T01:26:00.004-07:00

http://www.howtoaddurl.com
http://www.addurladd.com
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http://www.addurlsubmiturl.com
http://www.twitteraddurl.com
http://www.formsubmiturl.com
http://www.iwebseotool.com
http://addurltogooglesearch.com/
http://addacommentname.com/
http://thelinksubmitter.com/
http://howtouseseo.com/
http://whataredirectories.com/
http://addgoogle.com/
http://sitesubmit2.com/
http://directoryenquries.com/
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PPC Interview Question and Answer

2012-11-29T03:41:00.002-08:00

Q) Based on which Google places ads in first place?
(A) Google decides to give rank 1 in ads depending upon CTR(quality score) x CPC bid.
(Q) What is CTR?
(A) CTR – Click through rate. It is number of times your ad is clicked.
(Q) How many campaigns can I run in one adwords account?
(A) 25 Campaigns
(Q) How many adgroups can I run under one campaign?
(A) 2000 adgroups
(Q) How many ads can I run per adgroup?
(A) 50 ads per adgroup
(Q) How much characters can I place in one ad?

(A) For one ad 4 rows are given

25 characters for headline

35 characyers per text row(including URL)

(Q) How can you Improve Conversion Rates?
(A) Creating and testing campaign with different keywords and choosing that perform well
(Q) IS PPC effective advertisement for search engine rankings?
(A) Google or any other search engine don`t mix PPC ads with search rankings.
(Q) What is Quality Score?
(A) Quality Score is Score give to your ads that attain by keywords. The Higher the quality score the less you need to pay for a Top Position of your ads. It is given upon CTR.
(Q) Which companies are offering PPC advertisement?
(A) Yahoo, MSN and Google are among top most PPC advertisers.
(Q) What is Page rank? Explain it?
(A) Google page rank algorithm helps search engines to realize the value of a page. It ranks your website on basis of quality links it has. It is given by Google depending upon keyword, backlink sites, and content.
(Q) Why I need to go for adwords for PPC?
(A) Because Adwords assures that 80% of internet users sees your product or service.
(Q) How to achieve good CTR?
(A)Here are few things that need to be kept in mind for CTR

Target your ads to right audience
Select correct keyword matching
See that you target your ads by location and language
Create different Ad Groups for different search phrases/keywords
Calculate how much you can afford for the day
test your ads on daily basis, change if you don`t get any response from users
Give google users a good reason to click your ad

Latest Seo Interview Question

2012-11-29T03:28:00.003-08:00

1. Give me a description of your general SEO experience.
2. Can you write HTML code by hand?
3. Could you briefly explain the Page Rank algorithm?
4. What do you think of Page Rank?
5. What do you think of using XML sitemaps?
6. What are your thoughts on the direction of Web 2.0 technologies with regards to SEO?
7. What SEO tools do you regularly use?
8. Under what circumstances would you look to exclude pages from search engines using robots.txt vs. Meta robots tag?
9. What areas do you think are currently the most important in organically ranking a site?
10. Have you ever had something you’ve written reach the front-page of Digg? Sphinn? Or be stumbled?
11. Explain to me what META tags matter in today’s world.
12. Explain various steps that you would take to optimize a website?
13. If the company whose site you’ve been working for has decided to move all of its content to a new domain, what steps would you take?
14. Rate from 1 to 10, tell me the most important “on page” elements
15. Review the code of past clients/company websites where SEO was performed.
16. What do you think about link buying?
17. What is Latent Semantic Analysis (LSI Indexing)?
18. What is Phrase Based Indexing and Retrieval and what roles does it play?
19. What is the difference between SEO and SEM?
20. What kind of strategies do you normally implement for back links?
21. What role do social media play in an SEO strategy?
22. What things wouldn’t you to do increase rankings because the risk of penalty is too high?
23. What’s the difference between Page Rank and Toolbar Page Rank?
Analysis
1. Are you familiar with web analytics and what packages are your familiar with?
2. From an analytics perspective, what is different between users from organic search results vs. a type-in user?
3. How do you distinguish the results of your search optimization work from a seasonal change in traffic patterns?
4. How do you evaluate whether an SEO campaign is working?
5. What does competitive analysis mean to you and what techniques do you use?
6. If you’ve done 6 months of SEO for a site and yet there haven’t been any improvements, how would you go about diagnosing the problem?
7. How many target keywords should a site have?
8. How do *you* help a customer decide how to their budget between organic SEO and pay-per-click SEM?
9. You hear a rumor that Google is weighting the HTML LAYER tag very heavily in ranking the relevance of its results – how does this affect your work?
10. Why does Google rank Wikipedia for so many topics?
Industry Involvement
1. Do you currently do SEO on your own sites? Do you operate any blogs? Do you currently do any freelance work and do you plan on continuing it?
2. What are some challenges facing the SEO industry?
3. What industry sites, blogs, and forums do you regularly read?
4. Who are the two key people – who started Google?
5. If you were bidding on a contract, what competitor would you most worry about?
Open-Ended
1. Tell me your biggest failure in an SEO project
2. What areas of SEO do you most enjoy?
3. In what areas of SEO are you strongest?
4. In what areas of SEO are you weakest?
5. How do you handle a client who does not implement your SEO recommendations?
6. Can you get “xyz”? Company listed for the keyword “Google”? In the first page?
7. What do you think is different about working for an SEO agency vs. doing SEO in-house?
Open-ended SEO questions
1. What is your favourite aspect of SEO?
2. What is the most difficult aspect of SEO for you?
3. What has been your biggest mistake in optimizing a website for search engines?
4. What has been you biggest success in SEO?
5. What business sectors have you previously worked in as a SEO?
6. What is the most competitive sector you have worked in as a SEO specialist?
7. What is your favourite SEO website/blog, and why?
8. Who do you most respect in the SEO industry, and why?
9. Which website do you go to learn something new every time?
Analytics
1. What Analytics packages have you used?
2. Talk me through the process of setting conversion goals?
Algorithms
1. Please explain the Page Rank algorithm…
2. What is the most important aspect to you of the Page Rank algorithm for link-building?
3. What is page segmentation?
4. What are LSI / LSA and its relevance to SEO?
5. Explain to me how phrase-base algorithms work? Clustering?
6. Describe any perceived differences in the main search engines?
Keywords
1. What process do you typically go through when researching keywords?
2. How could this process be improved?
3. How do you carry out competitive analysis of keywords/SERPs as part of the keyword research process?
4. When targeting keywords on-page, discuss some considerations you might make?
Accessibility
1. What factors hinder search engines access to a website’s content?
2. What is the most responsible way of using Flash?
3. Tell me how you might use the Robots.txt file?
4. What is the difference between an xml sitemap and an html sitemap?
On-page Ranking Factors
1. If you were reviewing a landing page, what on-page ranking factors would you consider?
2. How would you analyse the strength of that page as part of the site?
3. Are you competent with HTML and CSS?
Onsite Ranking Factors
1. Talk me through factors you would consider in building an optimized website. (Possible answers might include the discussion around information architecture, site structure, title tags, link structures, keyword relevance, etc).
2. What are onsite ranking factors for building a successful landing page strategy?
3. Please provide examples of black hat SEO techniques? 4. What are your thoughts on black hat SEO techniques? What, if any, have you used, or tested?
Offsite Ranking Factors
1. What would the perfect inbound link look like?
2. What do you like and not like about link-building?
3. Explain to me your involvement in link-building in the past?
4. What approach to link-building have you had most success?
Link bait Development and Marketing
1. Would you consider yourself as creative?
2. Have you ever successfully carried out a link bait campaign for a client / in-house? What was the success?
3. Talk me through the process you might go through in developing a link bait strategy?
Copywriting
1. Are you confident writing and publishing content online?
2. Please provide examples of the content that you have written. What was the purpose of this content and what keywords were you targeting?
SEO Tools
1. What keyword research tools do you use and why?
2. What is your favourite ‘SEO tool’? Why?
3. Do you think SEO tools are effective in competitive markets? Why?
Testing
1. Have you carried-out split-testing / multivariate testing of content?
2. What did you learn from this process?
Image Optimization
1. What factors can you do to encourage the chance of ranking for images?
2. What is hot linking? How can this be successfully optimized?
Video optimization
1. Have you ever carried out video optimization?
2. What are a few considerations of optimizing video content?

List of Social Bookmarking Web Sites

2012-11-28T21:25:00.000-08:00

No.	Website URL	Page Rank
#1	Diigo.com
#2	Stumbleupon.com
#3	Digg.com
#4	Reddit.com
#5	Slashdot.org
#6	Delicious.com
#7	Fark.com
#8	Technorati.com
#9	Citeulike.org
#10	Connotea.org

Data Structure Inteview Question and Answer

2012-11-28T21:20:00.000-08:00

1) What is data structure?
Data structure refers to the way data is organized and manipulated. It seeks to find ways to make data access more efficient. When dealing with data structure, we not only focus on one piece of data, but rather different set of data and how they can relate to one another in an organized manner.
2) Differentiate file structure from storage structure.
Basically, the key difference is the memory area that is being accessed. When dealing with the structure that resides the main memory of the computer system, this is referred to as storage structure. When dealing with an auxiliary structure, we refer to it as file structure.
3) When is a binary search best applied?
A binary search is an algorithm that is best applied to search a list when the elements are already in order or sorted. The list is search starting in the middle, such that if that middle value is not the target search key, it will check to see if it will continue the search on the lower half of the list or the higher half. The split and search will then continue in the same manner.
4) What is a linked list?
A linked list is a sequence of nodes in which each node is connected to the node following it. This forms a chain-like link of data storage.
5) How do you reference all the elements in a one-dimension array?
To do this, an indexed loop is used, such that the counter runs from 0 to the array size minus one. In this manner, we are able to reference all the elements in sequence by using the loop counter as the array subscript.
6) In what areas do data structures applied?
Data structure is important in almost every aspect where data is involved. In general, algorithms that involve efficient data structure is applied in the following areas: numerical analysis, operating system, A.I., compiler design, database management, graphics, and statistical analysis, to name a few.
7) What is LIFO?
LIFO is short for Last In First Out, and refers to how data is accessed, stored and retrieved. Using this scheme, data that was stored last , should be the one to be extracted first. This also means that in order to gain access to the first data, all the other data that was stored before this first data must first be retrieved and extracted.
8 ) What is a queue?
A queue is a data structure that can simulates a list or stream of data. In this structure, new elements are inserted at one end and existing elements are removed from the other end.
9) What are binary trees?

A binary tree is one type of data structure that has two nodes, a left node and a right node. In programming, binary trees are actually an extension of the linked list structures.
10) Which data structure is applied when dealing with a recursive function?
Recursion, which is basically a function that calls itself based on a terminating condition, makes use of the stack. Using LIFO, a call to a recursive function saves the return address so that it knows how to return to the calling function after the call terminates.
11) What is a stack?
A stack is a data structure in which only the top element can be accessed. As data is stored in the stack, each data is pushed downward, leaving the most recently added data on top.
12) Explain Binary Search Tree
A binary search tree stores data in such a way that they can be retrieved very efficiently. The left subtree contains nodes whose keys are less than the node’s key value, while the right subtree contains nodes whose keys are greater than or equal to the node’s key value. Moreover, both subtrees are also binary search trees.
13) What are multidimensional arrays?
Multidimensional arrays make use of multiple indexes to store data. It is useful when storing data that cannot be represented using a single dimensional indexing, such as data representation in a board game, tables with data stored in more than one column.
14) Are linked lists considered linear or non-linear data structure?
It actually depends on where you intend to apply linked lists. If you based it on storage, a linked list is considered non-linear. On the other hand, if you based it on access strategies, then a linked list is considered linear.
15) How does dynamic memory allocation help in managing data?
Aside from being able to store simple structured data types, dynamic memory allocation can combine separately allocated structured blocks to form composite structures that expand and contract as needed.
16) What is FIFO?
FIFO is short for First-in, First-out, and is used to represent how data is accessed in a queue. Data has been inserted into the queue list the longest is the one that is removed first.
17) What is an ordered list?
An ordered list is a list in which each node’s position in the list is determined by the value of its key component, so that the key values form an increasing sequence, as the list is traversed.
18) What is merge sort?
Merge sort takes a divide-and-conquer approach to sorting data. In a sequence of data, adjacent ones are merged and sorted to create bigger sorted lists. These sorted lists are then merged again to form an even bigger sorted list, which continuous until you have one single sorted list.
19) Differentiate NULL and VOID.
Null is actually a value, whereas Void is a data type identifier. A variable that is given a Null value simply indicates an empty value. Void is used to identify pointers as having no initial size.
20) What is the primary advantage of a linked list?
A linked list is a very ideal data structure because it can be modified easily. This means that modifying a linked list works regardless of how many elements are in the list.
21) What is the difference between a PUSH and a POP?
Pushing and popping applies to the way data is stored and retrieved in a stack. A push denotes data being added to it, meaning data is being “pushed” into the stack. On the other hand, a pop denotes data retrieval, and in particular refers to the topmost data being accessed.
22) What is a linear search?
A linear search refers to the way a target key is being searched in a sequential data structure. Using this method, each element in the list is checked and compared against the target key, and is repeated until found or if the end of the list has been reached.
23) How does variable declaration affect memory allocation?
The amount of memory to be allocated or reserved would depend on the data type of the variable being declared. For example, if a variable is declared to be of integer type, then 32 bits of memory storage will be reserved for that variable.
24) What is the advantage of the heap over a stack?
Basically, the heap is more flexible than the stack. That’s because memory space for the heap can be dynamically allocated and de-allocated as needed. However, memory of the heap can at times be slower when compared to that stack.
25) What is a postfix expression?
A postfix expression is an expression in which each operator follows its operands. The advantage of this form is that there is no need to group sub-expressions in parentheses or to consider operator precedence.
26) What is Data abstraction?
Data abstraction is a powerful tool for breaking down complex data problems into manageable chunks. This is applied by initially specifying the data objects involved and the operations to be performed on these data objects without being overly concerned with how the data objects will be represented and stored in memory.
27) How do you insert a new item in a binary search tree?
Assuming that the data to be inserted is a unique value (that is, not an existing entry in the tree), check first if the tree is empty. If it’s empty, just insert the new item in the root node. If it’s not empty, refer to the new item’s key. If it’s smaller than the root’s key, insert it into the root’s left subtree, otherwise, insert it into the root’s right subtree.
28) How does a selection sort work for an array?
The selection sort is a fairly intuitive sorting algorithm,, though not necessarily efficient. To perform this, the smallest element is first located and switched with the element at subscript zero, thereby placing the smallest element in the first position. The smallest element remaining in the subarray is then located next with subscripts 1 through n-1 and switched with the element at subscript 1, thereby placing the second smallest element in the second position. The steps are repeated in the same manner till the last element.
29) How do signed and unsigned numbers affect memory?
In the case of signed numbers, the first bit is used to indicate whether positive or negative, which leaves you with one bit short. With unsigned numbers, you have all bits available for that number. The effect is best seen in the number range (unsigned 8 bit number has a range 0-255, while 8-bit signed number has a range -128 to +127.
30) What is the minimum number of nodes that a binary tree can have?
A binary tree can have a minimum of zero nodes, which occurs when the nodes have NULL values. Furthermore, a binary tree can also have 1 or 2 nodes.
31) What are dynamic data structures?
Dynamic data structures are structures that expand and contract as a program runs. It provides a flexible means of manipulating data because it can adjust according to the size of the data.
32) In what data structures are pointers applied?
Pointers that are used in linked list have various applications in data structure. Data structures that make use of this concept include the Stack, Queue, Linked List and Binary Tree.
33) Do all declaration statements result in a fixed reservation in memory?
Most declarations do, with the exemption of pointers. Pointer declaration does not allocate memory for data, but for the address of the pointer variable. Actual memory allocation for the data comes during run-time.
34) What are ARRAYs?
When dealing with arrays, data is stored and retrieved using an index that actually refers to the element number in the data sequence. This means that data can be accessed in any order. In programming, an array is declared as a variable having a number of indexed elements.
35) What is the minimum number of queues needed when implementing a priority queue?
The minimum number of queues needed in this case is two. One queue is intended for sorting priorities while the other queue is intended for actual storage of data.
36) Which sorting algorithm is considered the fastest?
There are many types of sorting algorithms: quick sort, bubble sort, balloon sort, radix sort, merge sort, etc. Not one can be considered the fastest because each algorithm is designed for a particular data structure and data set. It would depend on the data set that you would want to sort.
37) Differentiate STACK from ARRAY.
Data that is stored in a stack follows a LIFO pattern. This means that data access follows a sequence wherein the last data to be stored will the first one to be extracted. Arrays, on the other hand, does not follow a particular order and instead can be accessed by referring to the indexed element within the array.
38) Give a basic algorithm for searching a binary search tree.
1. if the tree is empty, then the target is not in the tree, end search
2. if the tree is not empty, the target is in the tree
3. check if the target is in the root item
4. if target is not in the root item, check if target is smaller than the root’s value
5. if target is smaller than the root’s value, search the left subtree
6. else, search the right subtree
39) What is a dequeue?
A dequeue is a double-ended queue. This is a structure wherein elements can be inserted or removed from either end.
40) What is a bubble sort and how do you perform it?
A bubble sort is one sorting technique that can be applied to data structures such as an array. It works by comparing adjacent elements and exchanges their values if they are out of order. This method lets the smaller values “bubble” to the top of the list, while the larger value sinks to the bottom.
41) What are the parts of a linked list?
A linked list typically has two parts: the head and the tail. Between the head and tail lie the actual nodes, with each node being linked in a sequential manner.
42) How does selection sort work?
Selection sort works by picking the smallest number from the list and placing it at the front. This process is repeated for the second position towards the end of the list. It is the simplest sort algorithm.
43) What is a graph?
A graph is one type of data structure that contains a set of ordered pairs. These ordered pairs are also referred to as edges or arcs, and are used to connect nodes where data can be stored and retrieved.
44) Differentiate linear from non linear data structure.
Linear data structure is a structure wherein data elements are adjacent to each other. Examples of linear data structure include arrays, linked lists, stacks and queues. On the other hand, non-linear data structure is a structure wherein each data element can connect to more than two adjacent data elements. Examples of non linear data structure include trees and graphs.
45) What is an AVL tree?
An AVL tree is a type of binary search tree that is always in a state of partially balanced. The balance is measured as a difference between the heights of the subtrees from the root. This self-balancing tree was known to be the first data structure to be designed as such.
46) What are doubly linked lists?
Doubly linked lists are a special type of linked list wherein traversal across the data elements can be done in both directions. This is made possible by having two links in every node, one that links to the next node and other one that links to the previous node.
47) What is Huffman’s algorithm?
Huffman’s algorithm is associated in creating extended binary trees that has minimum weighted path lengths from the given weights. It makes use of a table that contains frequency of occurrence for each data element.
48) What is Fibonacci search?
Fibonacci search is a search algorithm that applies to a sorted array. It makes use of a divide-and-conquer approach that can greatly reduce the time needed in order to reach the target element.
49) Briefly explain recursive algorithm.
Recursive algorithm targets a problem by dividing it into smaller, manageable sub-problems. The output of one recursion after processing one sub-problem becomes the input to the next recursive process.
50) How do you search for a target key in a linked list?
To find the target key in a linked list, you have to apply sequential search. Each node is traversed and compared with the target key, and if it is different, then it follows the link to the next node. This traversal continues until either the target key is found or if the last node is reached.

PHP Interview Question and Answer

2012-11-28T21:18:00.002-08:00

1) What is PHP?

PHP is a web language based on scripts that allows developers to dynamically create generated web pages.

2) What does the initials of PHP stand for?

PHP means PHP: Hypertext Preprocessor.

3) Which programming language does PHP resemble to?

PHP syntax resembles Perl and C

4) What does PEAR stands for?

PEAR means “PHP Extension and Application Repository”. it extends PHP and provides a higher level of programming for web developers.

5) What is the actually used PHP version?

Version 5 is the actually used version of PHP.

6) How do you execute a PHP script from the command line?

Just use the PHP command line interface (CLI) and specify the file name of the script to be executed as follows:

1	php script.php

7) How to run the interactive PHP shell from the command line interface?

Just use the PHP CLI program with the option -a as follows:

php -a

8 What are the correct and the most two common way to start and finish a PHP block of code?

The two most common ways to start and finish a PHP script are: <?php [ --- PHP code---- ] ?> and <? [--- PHP code ---] ?>

9) How can we display the output directly to the browser?

To be able to display the output directly to the browser, we have to use the special tags <?= and ?>.

10) What is the main difference between PHP 4 and PHP 5?

PHP 5 presents many additional OOP (Object Oriented Programming) features.

11) Is multiple inheritance supported in PHP?

PHP includes only single inheritance, it means that a class can be extended from only one single class using the keyword ‘extended’.

12) What is the meaning of a final class and a final method?

‘final’ is introduced in PHP5. Final class means that this class cannot be extended and a final method cannot be overrided.

13) How comparison of objects is done in PHP5?

We use the operator ‘==’ to test is two object are instanced from the same class and have same attributes and equal values. We can test if two object are refering to the same instance of the same class by the use of the identity operator ‘===’.

14) How can PHP and HTML interact?

It is possible to generate HTML through PHP scripts, and it is possible to pass informations from HTML to PHP.

15) What type of operation is needed when passing values through a form or an URL?

If we would like to pass values througn a form or an URL then we need to encode and to decode them using htmlspecialchars() and urlencode().

16) How can PHP and Javascript interact?

PHP and Javascript cannot directly interacts since PHP is a server side language and Javascript is a client side language. However we can exchange variables since PHP is able to generate Javascript code to be executed by the browser and it is possible to pass specific variables back to PHP via the URL.

17) What is needed to be able to use image function?

GD library is needed to be able execute image functions.

18) What is the use of the function ‘imagetypes()’?

imagetypes() gives the image format and types supported by the current version of GD-PHP.

19) What are the functions to be used to get the image’s properties (size, width and height)?

The functions are getimagesize() for size, imagesx() for width and imagesy() for height.

20) How failures in execution are handled with include() and require() functions?

If the function require() cannot access to the file then it ends with a fatal error. However, the include() function gives a warning and the PHP script continues to execute.

21) What is the main difference between require() and require_once()?

require() and require_once() perform the same task except that the second function checks if the PHP script is already included or not before executing it.

(same for include_once() and include())

22) How can I display text with a PHP script?

Two methods are possible:

<?php

echo "Method 1";

print "Method 2";

23) How can we display information of a variable and readable by human with PHP?

To be able to display a human-readable result we use print_r().

24) How is it possible to set an infinite execution time for PHP script?

The set_time_limit(0) added at the beginning of a script sets to infinite the time of execution to not have the PHP error ‘maximum execution time exceeded’.It is also possible to specify this in the php.ini file.

25) What does the PHP error ‘Parse error in PHP – unexpected T_variable at line x’ means?

This is a PHP syntax error expressing that a mistake at the line x stops parsing and executing the program.

26) What should we do to be able to export data into an Excel file?

The most common and used way is to get data into a format supported by Excel. For example, it is possible to write a .csv file, to choose for example comma as separator between fields and then to open the file with Excel.

27) What is the function file_get_contents() usefull for?

file_get_contents() lets reading a file and storing it in a string variable.

28) How can we connect to a MySQL database from a PHP script?

To be able to connect to a MySQL database, we must use mysql_connect() function as follows:

<?php

$database = mysql_connect("HOST", "USER_NAME", "PASSWORD");

mysql_select_db("DATABASE_NAME",$database);

29) What is the function mysql_pconnect() usefull for?

mysql_pconnect() ensure a persistent connection to the database, it means that the connection do not close when the the PHP script ends.

30) How the result set of Mysql be handled in PHP?

The result set can be handled using mysql_fetch_array, mysql_fetch_assoc, mysql_fetch_object or mysql_fetch_row.

31) How is it possible to know the number of rows returned in result set?

The function mysql_num_rows() returns the number of rows in a result set.

32) Which function gives us the number of affected entries by a query?

mysql_affected_rows() return the number of entries affected by an SQL query.

33) What is the difference between mysql_fetch_object() and mysql_fetch_array()?

The mysql_fetch_object() function collects the first single matching record where mysql_fetch_array() collects all matching records from the table in an array.

34) How can we access the data sent through the URL with the GET method?

In order to access the data sent via the GET method, we you use $_GET array like this:

www.url.com?var=value
$variable = $_GET["var"]; this will now contain ‘value’

35) How can we access the data sent through the URL with the POST method?

To access the data sent this way, you use the $_POST array.

Imagine you have a form field called ‘var’ on the form, when the user clicks submit to the post form, you can then access the value like this:

$_POST["var"];

36) How can we check the value of a given variable is a number?

It is possible to use the dedicated function, is_numeric() to check whether it is a number or not.

37) How can we check the value of a given variable is alphanumeric?

It is possible to use the dedicated function, ctype_alpha() to check whether it is an alphanumeric value or not.

38) How do I check if a given variable is empty?

If we want to check whether a variable has a value or not, it is possible to use the empty() function.

39) What does the unlink() function means?

The unlink() function is dedicated for file system handling. It simply deletes the file given as entry.

40) What does the unset() function means?

The unlink() function is dedicated for variable management. It will make a variable undefined.

41) How do I escape data before storing it into the database?

addslashes function enables us to escape data before storage into the database.

42) How is it possible to remove escape characters from a string?

The stripslashes function enables us to remove the escape characters before apostrophes in a string.

43) How can we automatically escape incoming data?

We have to enable the Magic quotes entry in the configuration file of PHP.

44) What does the function get_magic_quotes_gpc() means?

The function get_magic_quotes_gpc() tells us whether the magic quotes is switched on or no.

45) Is it possible to remove the HTML tags from data?

The strip_tags() function enables us to clean a string from the HTML tags.

46) what is the static variable in function useful for?

A static variable is defined within a function only the first time and its value can be modified during function calls as follows:

<?php

function testFunction() { static $testVariable = 1;

echo $testVariable;

$testVariable++;

}

testFunction(); //1

testFunction(); //2

testFunction(); //3

47) How can we define a variable accessible in functions of a PHP script?

This feature is possible using the global keyword.

48) How is it possible to return a value from a function?

A function returns a value using the instruction ‘return $value;’.

49) What is the most convenient hashing method to be used to hash passwords?

It is preferable to use crypt() which natively supports several hashing algorithms or the function hash() which supports more variants than crypt() rather than using the common hashing algorithms such as md5, sha1 or sha256 because they are conceived to be fast. hence, hashing passwords with these algorithms can vulnerability.

50) Which cryptographic extension provide generation and verification of digital signatures?

The PHP-openssl extension provides several cryptographic operations including generation and verification of digital signatures.

51) How a constant is defined in a PHP script?

The define() directive lets us defining a constant as follows:

define (“ACONSTANT”, 123);

52) How can you pass a variable by reference?

To be able to pass a variable by reference, we use an ampersand in front of it, as follows $var1 = &$var2

53) Will a comparison of an integer 12 and a string “13″ work in PHP?

“13″ and 12 can be compared in PHP since it casts everything to the integer type.

54) How is it possible to cast types in PHP?

The name of the output type have to be specified in parentheses before the variable which is to be cast as follows:

* (int), (integer) – cast to integer

* (bool), (boolean) – cast to boolean

* (float), (double), (real) – cast to float

* (string) – cast to string

* (array) – cast to array

* (object) – cast to object

55) When a conditional statement is ended with an endif?

When the original if was followed by : and then the code block without braces.

56) How is the ternary conditional operator used in PHP?

It is composed of three expressions: a condition, and two operands describing what instruction should be performed when the specified condition is true or false as follows:

Expression_1 ? Expression_2 : Expression_3;

57) What is the function func_num_args() used for?

The function func_num_args() is used to give the number of parameters passed into a function.

58) If the variable $var1 is set to 10 and the $var2 is set to the character var1, what’s the value of $$var2?

$$var2 contains the value 10.

59) What does accessing a class via :: means?

:: is used to access static methods that do not require object initialization.

60) In PHP, objects are they passed by value or by reference?

In PHP, objects passed by value.

61) Are Parent constructors called implicitly inside a class constructor?

No, a parent constructor have to be called explicitly as follows:

parent::constructor($value)

62) What’s the difference between __sleep and __wakeup?

__sleep returns the array of all the variables that need to be saved, while __wakeup retrieves them.

63) What is faster?

1- Combining two variables as follows:

$variable1 = ‘Hello ‘;

$variable2 = ‘World’;

$variable3 = $variable1.$variable2;

2- $variable3 = “$variable1$variable2″;

$variable3 will contain “Hello World”. The first code is faster than the second code especially for large large sets of data.

64) what is the definition of a session?

A session is a logical object enabling us to preserve temporary data across multiple PHP pages.

65) How to initiate a session in PHP?

The use of the function session_start() lets us activating a session.

66) How is it possible to propagate a session id?

It is possible to propagate a session id via cookies or URL parameters.

67) What is the meaning of a Persistent Cookie?

A persistent cookie is permanently stored in a cookie file on the browser’s computer. By default, cookies are temporary and are erased if we close the browser.

68) When sessions ends?

Sessions automatically ends when the PHP script finishs executing, but can be manually ended using the session_write_close().

69) What is the difference between session_unregister() and session_unset()?

The session_unregister() function unregister a global variable from the current session and the session_unset() function free all session variables.

70) What does $GLOBALS means?

$GLOBALS is associative array including references to all variables which are currently defined in the global scope of the script.

71) What does $_SERVER means?

$_SERVER is an array including information created by the web server such as paths, headers, and script locations.

72) What does $_FILES means?

$_FILES is an associative array composed of items sent to the current script via the HTTP POST method.

73) What is the difference between $_FILES['userfile']['name'] and $_FILES['userfile']['tmp_name']?

$_FILES['userfile']['name'] represents the original name of the file on the client machine,

$_FILES['userfile']['tmp_name'] represents the temporary filename of the file stored on the server.

74) How can we get the error when there is a problem to upload a file?

$_FILES['userfile']['error'] contains the error code associated with the uploaded file.

75) How can we change the maximum size of the files to be uploaded?

We can change the maximum size of files to be uploaded by changing upload_max_filesize in php.ini.

76) What does $_ENV means?

$_ENV is an associative array of variables sent to the current PHP script via the environment method.

77) What does $_COOKIE means?

$_COOKIE is an associative array of variables sent to the current PHP script using the HTTP Cookies.

78) What does the scope of variables means?

The scope of a variable is the context within which it is defined. For the most part all PHP variables only have a single scope. This single scope spans included and required files as well.

79) what the difference between the ‘BITWISE AND’ operator and the ‘LOGICAL AND’ operator?

$a and $b: TRUE if both $a and $b are TRUE.

$a & $b: Bits that are set in both $a and $b are set.

80) What are the two main string operators?

The first is the concatenation operator (‘.’), which returns the concatenation of its right and left arguments. The second is (‘.=’), which appends the argument on the right to the argument on the left.

81) What does the array operator ‘===’ means?

$a === $b TRUE if $a and $b have the same key/value pairs in the same order and of the same types.

82) What is the differences between $a != $b and $a !== $b?

!= means inequality (TRUE if $a is not equal to $b) and !== means non-identity (TRUE if $a is not identical to $b).

83) How can we determine whether a PHP variable is an instantiated object of a certain class?

To be able to verify whether a PHP variable is an instantiated object of a certain class we use instanceof.

84) What is the goto statement useful for?

The goto statement can be placed to enable jumping inside the PHP program. The target is pointed by a label followed by a colon, and the instruction is specified as a goto statement followed by the desired target label.

85) what is the difference between Exception::getMessage and Exception::getLine ?

Exception::getMessage lets us getting the Exception message and Exception::getLine lets us getting the line in which the exception occurred.

86) What does the expression Exception::__toString means?

Exception::__toString gives the String representation of the exception.

87) How is it possible to parse a configuration file?

The function parse_ini_file() enables us to load in the ini file specified in filename, and returns the settings in it in an associative array.

88) How can we determine whether a variable is set?

The boolean function isset determines if a variable is set and is not NULL.

89) What is the difference between the functions strstr() and stristr()?

The string function strstr(string allString, string occ) returns part of allString from the first occurrence of occ to the end of allString. This function is case-sensitive. stristr() is identical to strstr() except that it is case insensitive.

90) what is the difference between for and foreach?

for is expressed as follows:

for (expr1; expr2; expr3)

statement

The first expression is executed once at the beginning. In each iteration, expr2 is evaluated. If it is TRUE, the loop continues and the statements inside for are executed. If it evaluates to FALSE, the execution of the loop ends. expr3 is tested at the end of each iteration.

However, foreach provides an easy way to iterate over arrays and it is only used with arrays and objects.

91) Is it possible to submit a form with a dedicated button?

It is possible to use the document.form.submit() function to submit the form. For example: <input type=button value=”SUBMIT” onClick=”document.form.submit()”>

92) What is the difference between ereg_replace() and eregi_replace()?

The function eregi_replace() is identical to the function ereg_replace() except that it ignores case distinction when matching alphabetic characters.

93) Is it possible to protect special characters in a query string?

Yes, we use the urlencode() function to be able to protect special characters.

94) What are the three classes of errors that can occur in PHP?

The three basic classes of errors are notices (non-critical), warnings (serious errors) and fatal errors (critical errors).

95) What is the difference between characters \034 and \x34?

\034 is octal 34 and \x34 is hex 34.

96) How can we pass the variable through the navigation between the pages?

It is possible to pass the variables between the PHP pages using sessions, cookies or hidden form fields.

97) Is it possible to extend the execution time of a php script?

The use of the set_time_limit(int seconds) enables us to extend the execution time of a php script. The default limit is 30 seconds.

98) Is it possible to destroy a cookie?

Yes, it is possible by setting the cookie with a past expiration time.

99) What is the default session time in php?

The default session time in php is until closing of browser

100) Is it possible to use COM component in PHP?

Yes, it’s possible to integrate (Distributed) Component Object Model components ((D)COM) in PHP scripts which is provided as a framework.

XML Interview Question and Answer

2012-11-28T21:17:00.003-08:00

What is XML?
The Extensible Markup Language (XML) is a general-purpose specification for creating custom markup languages.[1] It is classified as an extensible language, because it allows the user to define the mark-up elements. XML’s purpose is to aid information systems in sharing structured data.

What is the version information in XML?
The root element can be preceded by an optional XML declaration element stating what XML version is in use (normally 1.0); it might also contain character encoding and external dependencies information.

What is ROOT element in XML?
XML documents must contain one element that is the parent of all other elements. This element is called the root element.

If XML does not have closing tag will it work?
All XML Elements Must Have a Closing Tag otherwise it will produce error while accessing or parsing.
Is XML case sensitive?

Yes it is. XML tags are case sensitive. With XML, the tag is different from the tag . Opening and closing tags must be written with the same case.
What’s the difference between XML and HTML?
On the surface, XML and HTML look similar. Both use tags (such as or ) and attributes (such as align=”left” or type=”personal”) to add information to the content. In fact, a carefully prepared HTML document can double as an XML document. The difference is that HTML is a well-defined set of elements and attributes. For example, the following is a well-formed XML document, but because it only uses tags that are defined in HTML, it’s also an HTML document:On the other hand, HTML has somewhat looser rules than XML, so some HTML documents are not well-formed XML documents.
Is XML meant to replace HTML?
xml is a portable document structure, which is not really for presentation. XSL or CSS may replace html, but really xml is meant to be a storage medium. It is like asking if databases will replace html. The one aspect that makes this whole thing blurry is that html and now Xhtml is a subset of xml. It is just used to make documents render in browsers.
Can you explain why your project needed XML?
1. If we having huge datas to be transferred instead of sending all those datas as dataset you can opt xml.
2. XML is easy to parse and it enables a faster accessing of datas.
3. Case sensitiveness is an additional advantage in validating the authentication for the user.
4. XML can be passed irrespective of OS, port and protocol.
What is DTD (Document Type definition)?
A Document Type Definition (DTD) defines the legal building blocks of an XML document. It defines the document structure with a list of legal elements and attributes.A DTD can be declared inline inside an XML document, or as an external reference Although XML allows you to invent as many different elements and attributes as you need, these elements and attributes, as well as their contents and the documents that contain them, must all follow certain rules in order to be well-formed. If a document is not well-formed, any attempts to read it or render it will fail.

What is a valid XML?
XML that meets the constraints defined by its Document Type Declaration.

11) What is CDATA section in XML?
CDATA Sections are used to escape blocks of text containing characters which would otherwise be recognized as markup. All tags and entity references are ignored by an XML processor that treats them just like any character data. CDATA blocks have been provided as a convenience measure when you want to include large blocks of special characters as character data, but you do not want to have to use entity references all the time

What is XSL?
Extensible Style Language is a style sheet language aimed at activities such as rearranging the document that are not supported by CSS, though XSL and CSS share the same underlying concepts. XSL can be used to style XML documents u sing sets of rules and definitions of actions to be applied. XSL is a specification from the W3C.

What is Element and attributes in XML?
The basic building blocks of XML Schemas are elements and attributes. Data types define the valid content that elements and attributes contain. When you create XML Schemas, you define the individual elements and attributes and assign valid types to them. Elements describe data, whereas attributes are like properties of an element, in that they provide further definition about the element the way that properties describe characteristics of objects and classes.
An element describes the data that it contains. Elements can also contain other elements and attributes.
An attribute is a named simple-type definition that cannot contain other elements. Attributes can also be assigned an optional default value and they must appear at the bottom of complex-type definitions. Additionally, if multiple attributes are declared, they may occur in any order.

What are the standard ways of parsing XML document?
DOM and SAX parsers are the standard ways for parsing XML document.

In What scenarios will you use a DOM parser and SAX parser?
In some scenarios, SAX is easily the better choice for quick, less-intensive parsing and processing. In others, the DOM provides an easy-to-use, clean interface to data in a desirable format. You, the developer, must always analyze your application and its purpose to make the correct decision as to which method to use, or how to use both in concert.

What is XSLT?
Extensible Stylesheet Language Transformations. A programming language specialized for the transformation of XML documents.

Define XPATH?
A query language used to identify a set of nodes within a XML document. Originally defined to be used with XSLT, it is also used by XPointer and a simple subset is used in the xs:key, xs:keyref, and xs:unique W3C XML Schema elements. The XQuery specification will be a superset of the second version of XPath. This version will use type information provided by W3C XML Schema

What is an XMLReader Class?
Represents a reader that provides fast, non-cached, forward-only access to XML data.
XmlReader provides forward-only, read-only access to a stream of XML data. The XmlReader class conforms to the W3C Extensible Markup Language (XML) 1.0 and the Namespaces in XML recommendations.

What is XMLTextReader?
The XmlTextReader class requires fast access to XML data. It does not require reading the entire document into memory via the Document Object Model (DOM). The class is derived from the XmlReader class and implements all the methods defined in the XmlReader class. The following are the functions of the XmlTextReader class:
* It enforces rules of a well-formed XML document.
* It does not provide any data validation in a document.
* It checks the Document Type Definition (DTD) and DocumentType nodes for their well-formed structure, but does not validate these nodes by using the DTD.

How do we access attributes using “XmlReader”?
The XmlReader class provides various methods and properties for reading attributes. Attributes are most commonly found on elements. However, they are also allowed on XML declaration and document type nodes.
When positioned on an element node, the MoveToAttribute methods enable you to go through the attribute list of the element. After MoveToAttribute has been called, the node properties—such as Name, NamespaceURI, Prefix, and so on—reflect the properties of that attribute, and not the containing element it belongs to.

What does XmlValidatingReader class do?
Represents a reader that provides document type definition (DTD), XML-Data Reduced (XDR) schema, and XML Schema definition language (XSD) validation.
XmlValidatingReader implements the XmlReader class and provides support for data validation. Use the Schemas property to have the reader validate by using schema files that are cached in an XmlSchemaCollection. The ValidationType property specifies what type of validation the reader should perform. Setting the property to ValidationType.None creates a non-validating reader.

What is XML?

XML is a markup language for specific documents which contain structured information. Structured information is both content and indication of contents role. Every document has specific structure. The mechanism which is used to determine structures in a document is known as a markup language. XML specification describes a perfect way to add markup o the documents.
• The abbreviation of XML is extensible markup language.
• XML is also a markup language which is same as HTML.
• XML is especially designed to describe data.
• The tags of XML are not predefined and the tags must be defined on your own.
• XML describes data using XML schema or Document Type Definition.
• XML is W3C recommendation.

• XML with XML or DTD Schema is especially designed to be self-descriptive.

Differentiate SAX and DOM parsers?

XML document is parsed using both SAX and DOM. Both have some advantages and disadvantages and are used in the programs based on the situation.
SAX:
• It parses node by node.
• XML is not stored in the memory.
• A node cannot be inserted or deleted.
• Traversing is from top to bottom.
DOM:
• It occupies more space in the memory.
• Complete document is stored in the memory before processing.
• Nodes can be inserted or deleted.
• Traversing is possible in any direction.

How an XML file is created?

XML can be created by plain text editor such as notepad or by .net model using various inbuilt methods such as XmlTextWriter.

Define XML namespace?

XML namespace offer a method to prevent element name conflicts. The collection of attribute names and element type is known as a XML namespace. A reasonable argument is made that XML namespaces do not exist conceptual or physical entities.

Does XML language replace HTML?

No, HTML is not replaced by XML. Instead, it is an alternative which permits you to define own set of markup elements. XML is specially designed to make DTDs writing simpler than full SGML.

Describe XMLHttpRequest Object?

XMLHttpRequest is sued to:
• Update webpage without reloading.
• Data is requested from server after loading the page.
• Data is received from the server after loading the page.
• Data is sent to the server in the background.

XMLhttp=new XMLHttpRequest();

Which software is used to process XML namespaces?

There is no special XML software.

Define XML namespace name?

XML namespace name is URI that identifies namespace uniquely. URIs are used as they are used widely and documented perfectly. Because, people allocate URIs under their control and it is easy to ensure no two XML namespaces are determined by same URI.

Differentiate XML and HTML?

XML:
• Slash
• These tags are defined by user
• Quotes
• Content driven end tags
HTML:
• Slash is not required
• Defined set of tags
• Quotes are not necessary
• Format driven

• End tags are not required

Define DOM?

The abbreviation of DOM is Document Object Model. It is an interface specification which is maintained by W3C DOM workgroup.

11. Why XML is vital in development?

Two constraints are removed by XML which hold back web developments: inflexible document type and dependence on a single.

Give basic issues to use attributes?

Some of the issues in using attributes are:
• Attributes do not have many values.
• Attributes do not contain tree structures
• Attributes cannot be expanded easily
Reading and maintaining attributes is very difficult. Elements are used for data. Attributes are used for information which is not related to data.

Give essential components of security and do signatures of XML provide it?

The following are three components:
• Message integrity
• Authentication
• Non-repudiation
Besides signature information, information is also present in the XML signature which describes key used to sign content.

Give examples for XML Editors?

• eNotepad
• XML Spy
• XML Pro
• XML Notepad
• XML Cooktop

Give XML Editor Benefits?

• While coding XML, it prevents from making mistakes.
• XML and HTML editors are same and they give syntax highlighting which helps with readability while coding.

• Closing tag is inserted automatically if you add an opening tag such as HTML editor.

What is the difference between SAX parser and DOM parser?
What is the difference between Schema and DTD?
How do you parse/validate the XML document?
What is XML Namespace?
What is Xpath?
What is XML template?
How would you produce PDF output using XSL’s?
What are the steps to transform XML into HTML using XSL?
What is XSL?
What is XSLT?

Sql Interview Questions and Answer

2012-11-21T21:42:00.003-08:00

A SUPER KEY is a set of one or more attributes that allows us to identify uniquely an entity in the entity set.

The PRIMARY KEY is the column(s) used to uniquely identify each row of a table. A table can have only one primary key.

A null signifies that a value is undefined or not known. This is not the same as a zero, a blank, or a default value. Instead, it indicates that a data value is absent.

A UNIQUE KEY is one or more columns that must be unique for each row of the table

A FOREIGN KEY is one or more columns whose values are based on the PRIMARY or CANDITATE KEY values from the database.
CANDIDATE KEY is a minimal superkey. A candidate key for a relation schema is a minimal set of attributes whose values uniquely identify tuples in the corresponding relation.

Metadata - are data about data but not the actual data

An entity - is an object with a physical existence.

A view - is a virtual table that is created when the view is invoked (by calling its name). The table doesn't actually exist, only the SQL statement that defines the table.

A set function - is a type of function that processes or calculates data and returns the appropriate values.

Data dictionary - is a repository of information describing the data in the database, that is the metadata. Data dictionary is a file that contains Metadata or data about data.

An entity type - defines a collection of entities that have same attribute Entity Set.

Entity set - is the collection of a particular entity type that are grouped into an Entity Set.

The REVOKE- statement is used to remove database privileges

What are the ways tablespaces can be managed and how do they differ?

Objects can be assigned to a table space. The related objects can be then grouped together. Table space can also be managed using extents. Extents consist of a specific number of contiguous data blocks. For the required extent, the free extent closest in size is determined.

Explain what are Oracle Catalog and Oracle Archive log?

Oracle catalog contains tables and views to get information about the database. It helps user to understand the available tables, attributes, constraints etc.

Oracle Archive log mode of a database in Oracle, ensures, the online redo logs are not overwritten before they are archived. This ensures that recovery is possible.

What are PCT Free and PCT Used? What is PCT increase parameter in segment?

PCTFREE is a parameter used to find how much space should be left in a database block for future updates. This means that if the PCTFREE = 20, new rows will be added in the block until it is 80% full.

PCTUSED is a parameter helps Oracle to find when it should consider a database block to be empty enough to be added to the freelist. This means that if the PCTFREE = 50, new rows will be not be added in the block until sufficient rows are deleted from the block so that it falls below 40% empty.

PCTINCREASE parameter is used to find how much will the each subsequent segment will grow. This value is in %.

What is dump destination? What are bdump, cdump and udump?

Trace files for Oracle processes are stored in dump destination.

Bdump- Oracle writes to the trace log and creates trace files for background processes in background dump destination. If this directory becomes full and more files cannot be written, debugging becomes difficult.

Cdump- Oracle writes core files and background processes in Core dump destination directory. If this directory becomes full and more files cannot be written, debugging becomes difficult.

Udump – Oracle creates trace files for the user processes in the User Dump directory if this directory becomes full and more files cannot be written, debugging becomes difficult.

How do you increase the performance of %LIKE operator?

LIKE% works the fastest because it uses the index to search on the column provided an index is specified on the column. Using % after LIKE, results in faster results.

Why use materialized view instead of a table

Materialized views are basically used to increase query performance since it contains results of a query. They should be used for reporting instead of a table for a faster execution.

Why and how the deadlock situation arises

A deadlock situation arises when two or more users wait for the same resource locked by one anther or two or more processes wait to update rows which are locked by other processes. Oracle if detects a deadlock, rolls back the session chosen by the deadlock victim.

What are standby databases? Difference between Physical and logical standby databases

A standby database is a replica of the original database. In order to keep both the database synchronized, archived redo logs can be used. It is mainly used in disaster protection. It can also be opened in read only mode which allows it to be used independently for reporting.

A logical standby database allows new database objects like tables, indexes to be added to the database. On the other hand, the physical standby database is a physical or structural copy of primary database. They can be opened in read only for disaster recovery.

What is Cache Fusion Technology?

In Cache fusion, multiple buffers join to act as one. It eliminates disk i/o operaions by making use of a scalable shared cache. It treats multiple buffer caches as one thereby resolving data consistency issues. Cash fusion technology can provide more resources and increases concurrency of users.

What is the difference between Cloning and Standby databases?

The clone database is a copy of the database which can be opened in read write mode. It is treated as a separate copy of the database that is functionally completely separate. The standby database is a copy of the production database used for disaster protection. In order to update the standby database; archived redo logs from the production database can be used. If the primary database is destroyed or its data becomes corrupted, one can perform a failover to the standby database, in which case the standby database becomes the new primary database.

What is dump destination? What are bdump, cdump and udump?

Trace files for Oracle processes are stored in dump destination.

Bdump- Oracle writes to the trace log and creates trace files for background processes in background dump destination. If this directory becomes full and more files cannot be written, debugging becomes difficult.

Cdump- Oracle writes core files and background processes in Core dump destination directory. If this directory becomes full and more files cannot be written, debugging becomes difficult.

Udump – Oracle creates trace files for the user processes in the User Dump directory if this directory becomes full and more files cannot be written, debugging becomes difficult.

What are PCT Free and PCT Used? What is PCT increase parameter in segment?

PCTINCREASE parameter is used to find how much will the each subsequent segment will grow. This value is in %

Explain what are Oracle Catalog and Oracle Archive log?

Oracle catalog contains tables and views to get information about the database. It helps user to understand the available tables, attributes, constraints etc.

Oracle Archive log mode of a database in Oracle, ensures, the online redo logs are not overwritten before they are archived. This ensures that recovery is possible

Transactional control commands?

COMMIT
ROLLBACK
SAVEPOINT
SET TRANSACTIONS

Drawbacks of file processing system?

Duplication of data, which leads to wastage of storage space and data inconsistency.

Types of data manipulation languages?

Procedural DMLs
Declarative DMLs

Physical and Logical data independence

In logical data independence, the conceptual schema can be changed without changing the external schema.

In physical data independence, the internal schema can be changed without changing the conceptual schema.

What is the difference between Delete and Truncate command in SQL
Delete command and truncate command both will delete the data, however the truncate command can not be rolled back as delete can be.
The delete command can be used for selected records using the where clause but with the truncate command we have to loose data. DELETE statement is a logged operation and hence takes more time then truncate.

What is the difference between a "where" clause and a "having" clause? -
"Where" is a kind of restiriction statement. You use where clause to restrict all the data from DB.Where clause is using before result retrieving. But Having clause is using after retrieving the data.Having clause is a kind of filtering command.

What is the basic form of a SQL statement to read data out of a table?

The basic form to read data out of table is ‘SELECT * FROM table_name; ‘ An answer: ‘SELECT * FROM table_name WHERE xyz= ‘whatever’;’ cannot be called basic form because of WHERE clause.

What is a "join"? -

‘join’ used to connect two or more tables logically with or without common field.

What structure can you implement for the database to speed up table reads?-

Follow the rules of DB tuning we have to: 1] properly use indexes ( different types of indexes) 2] properly locate different DB objects across different tablespaces, files and so on.3] create a special space (tablespace) to locate some of the data with special datatype ( for example CLOB, LOB and …)

What is "normalization"? "Denormalization"? Why do you sometimes want to denormalize? - Normalizing data means eliminating redundant information from a table and organizing the data so that future changes to the table are easier. Denormalization means allowing redundancy in a table. The main benefit of denormalization is improved performance with simplified data retrieval and manipulation. This is done by reduction in the number of joins needed for data processing.

Operating System Interview Question

2012-11-21T21:14:00.004-08:00

Operating System Interview Question

1. What is an operating system?
2. What are the various components of a computer system?
3. What is purpose of different operating systems?
4. What are the different operating systems?
5. What are operating system services?
6. What is a boot-strap program?
7. What is BIOS?
8. Explain the concept of the batched operating systems?
9. Explain the concept of the multi-programmed operating systems?
10. Explain the concept of the timesharing operating systems?
11. Explain the concept of the multi-processor systems or parallel systems?
12. Explain the concept of the Distributed systems?
13. Explain the concept of Real-time operating systems?
14. Define MULTICS?
15. What is SCSI?
16. What is a sector?
17. What is cache-coherency?
18. What are residence monitors?
19. What is dual-mode operation?
20. What are the operating system components?
21. What are operating system services?
22. What are system calls?
23. What is a layered approach and what is its advantage?
24. What is micro kernel approach and site its advantages?
25. What are a virtual machines and site their advantages?
26. What is a process?
27. What are the states of a process?
28. What are various scheduling queues?
29. What is a job queue?
30. What is a ready queue?
31. What is a device queue?
32. What is a long term scheduler & short term schedulers?
33. What is context switching?
34. What are the disadvantages of context switching?
35. What are co-operating processes?
36. What is a thread?
37. What are the benefits of multithreaded programming?
38. What are types of threads?
39. Which category the java thread do fall in?
40. What are multithreading models?
41. What is a P-thread?
42. What are java threads?
43. What is process synchronization?
44. What is critical section problem?
45. What is a semaphore?
46. What is bounded-buffer problem?
47. What is readers-writers problem?
48. What is dining philosophers’ problem?
49. What is a deadlock?
50. What are necessary conditions for dead lock?
51. What is resource allocation graph?
52. What are deadlock prevention techniques?
53. What is a safe state and a safe sequence?
54. What are the deadlock avoidance algorithms?
55. What are the basic functions of an operating system?
56. Explain briefly about, processor, assembler, compiler, loader, linker and the functions executed by them.
57. What is a Real-Time System?
58. What is the difference between Hard and Soft real-time systems?
59. What is virtual memory?
60. What is cache memory?
61.Differentiate between Complier and Interpreter?
62.What are different tasks of Lexical Analysis?
63. Why paging is used?
64. What is Context Switch?
65. Distributed Systems?
66.Difference between Primary storage and secondary storage?
67. What is CPU Scheduler?
68. What do you mean by deadlock?
69. What is Dispatcher?
70. What is Throughput, Turnaround time, waiting time and Response time?
71. Explain the difference between microkernel and macro kernel?
72.What is multi tasking, multi programming, multi threading?
73. Give a non-computer example of preemptive and non-preemptive scheduling?
74. What is starvation and aging?
75.Different types of Real-Time Scheduling?
76. What are the Methods for Handling Deadlocks?
77. What is a Safe State and its’ use in deadlock avoidance?
78. Recovery from Deadlock?
79.Difference between Logical and Physical Address Space?
80. Binding of Instructions and Data to Memory?
81. What is Memory-Management Unit (MMU)?
82. What are Dynamic Loading, Dynamic Linking and Overlays?
83. What is fragmentation? Different types of fragmentation?
84. Define Demand Paging, Page fault interrupt, and Trashing?
85. Explain Segmentation with paging?
86. Under what circumstances do page faults occur? Describe the actions taken by the operating system when a page fault occurs?
87. What is the cause of thrashing? How does the system detect thrashing? Once it detects thrashing, what can the system do to eliminate this problem?

OOPS Interview Question and Answer

2012-11-21T21:13:00.002-08:00

What is an Object in OOPS?

An object is a software bundle of variables and related methods. Objects are related to real life scenario. Class is the general thing and object is the specialization of general thingObjects is instance of classes.

Declaration of an Object in OOPs

ClassName objectName=new ClassName();

E.g.: Person objPerson= new Person();

An object is characterized by concepts like:

• Attribute

• Behavior

• Identity

2. What is an Attribute in OOPs?

• Attributes define the characteristics of a class.

• The set of values of an attribute of a particular object is called its state.

• In Class Program attribute can be a string or it can be a integer

3. What is a Behavior in OOPS?

• Every object has behavior

• In C#, behaviors of objects are written in methods.

• If a behavior of an object needs to be performed, then the corresponding method is called.

4. What is an Identity in OOPS?

• Each time an object is created the object identity is been defined.

• This identity is usually created using an identifier which is derived from the type of item

5. What is Encapsulation in OOPS?

• Encapsulation is one of the fundamental principles of object-oriented programming.

• Encapsulation is a process of hiding all the internal details of an object from the outside world

• Encapsulation is the ability to hide its data and methods from outside the world and only expose data and methods that are required

• Encapsulation is a protective barrier that prevents the code and data being randomly accessed by other code or by outside the class

• Encapsulation gives us maintainability, flexibility and extensibility to our code.

• Encapsulation makes implementation inaccessible to other parts of the program and protect from whatever actions might be taken outside the function or class.

• Encapsulation provides a way to protect data from accidental corruption

• Encapsulation hides information within an object

• Encapsulation is the technique or process of making the fields in a class private and providing access to the fields using public methods

• Encapsulation gives you the ability to validate the values before the object user change or obtain the value

• Encapsulation allows us to create a “black box” and protects an objects internal state from corruption by its clients.

There are two ways to create a validation process.

1. Using Assessors and Mutators

2. Using properties

Benefits of Encapsulation

• In Encapsulation fields of a class can be read-only or can be write-only

• A class can have control over in its fields

• A class can change data type of its fields anytime but users of this class do not need to change any code

6. What is Inheritance in OOPS?

• Inheritance, together with encapsulation and polymorphism, is one of the three primary characteristics (concept) of object-oriented programming

• Inheritance enables you to create new classes that reuse, extend, and modify the behavior that is defined in other classes

• The Class whose methods and variables are defined is called super class or base class

• The Class that inherits methods and variables are defined is called sub class or derived class

• Sometimes base class known as generalized class and derived class known as specialized class

• Keyword to declare inheritance is “:” (colon) in visual c#

Benefits of using Inheritance

• Once a behavior (method) or property is defined in a super class(base class),that behavior or property is automatically inherited by all subclasses (derived class).

• Code reusability increased through inheritance

• Inheritance provide a clear model structure which is easy to understand without much complexity

• Using inheritance, classes become grouped together in a hierarchical tree structure

• Code are easy to manage and divided into parent and child classes

7. What is Polymorphism in OOPS?

• Polymorphism is one of the primary characteristics (concept) of object-oriented programming

• Poly means many and morph means form. Thus, polymorphism refers to being able to use many forms of a type without regard to the details

• Polymorphism is the characteristic of being able to assign a different meaning specifically, to allow an entity such as a variable, a function, or an object to have more than one form

• Polymorphism is the ability to process objects differently depending on their data types

• Polymorphism is the ability to redefine methods for derived classes.

Types of Polymorphism

• Compile time Polymorphism

• Run time Polymorphism

8. What is Compile Time Polymorphism in OOPS?

• Compile time Polymorphism also known as method overloading

• Method overloading means having two or more methods with the same name but with different signatures

9. What is Run Time Polymorphism in OOPS?

• Run time Polymorphism also known as method overriding

• Method overriding means having two or more methods with the same name , same signature but with different implementation

10. What is Access Modifier in OOPS?

Access modifiers determine the extent to which a variable or method can be accessed from another class or object

The following five accessibility levels can be specified using the access modifiers

• Private

• Protected

• Internal

• Protected internal

• Public

C Language Interview Question

2012-11-21T21:12:00.001-08:00

1. What does static variable mean?

2. What is a pointer?

3. What is a structure?

4. What are the differences between structures and arrays?

5. In header files whether functions are declared or defined?

6. What are the differences between malloc() and calloc()?

7.What are macros? What are the advantages and disadvantages?

8. Difference between pass by reference and pass by value?

9. What is static identifier?

10. Where are the auto variables stored?

11. Where does global, static, local, register variables, free memory and C Program instructions get stored?

12. Difference between arrays and linked list?

13. What are enumerations?

14. Describe about storage allocation and scope of global, extern, static, local and register variables?

15. What are register variables? What are the advantage of using register variables?

16. What is the use of typedef?

17. Can we specify variable field width in a scanf() format string? If possible how?

18. Out of fgets() and gets() which function is safe to use and why?

19. Difference between strdup and strcpy?

20. What is recursion?

21. Differentiate between a for loop and a while loop? What are it uses?

22. What are the different storage classes in C?

23. Write down the equivalent pointer expression for referring the same element a[i][j][k][l]?

24. What is difference between Structure and Unions?

25. What the advantages of using Unions?

26. What are the advantages of using pointers in a program?

27. What is the difference between Strings and Arrays?

28. In a header file whether functions are declared or defined?

29. What is a far pointer? where we use it?

30. How will you declare an array of three function pointers where each function receives two ints and returns a float?

31. What is a NULL Pointer? Whether it is same as an uninitialized pointer?

32. What is a NULL Macro? What is the difference between a NULL Pointer and a NULL Macro?

33. What does the error ‘Null Pointer Assignment’ mean and what causes this error?

34. What is near, far and huge pointers? How many bytes are occupied by them?

35. How would you obtain segment and offset addresses from a far address of a memory location?

36. Are the expressions arr and *arr same for an array of integers?

37. Does mentioning the array name gives the base address in all the contexts?

38. Explain one method to process an entire string as one unit?

39. What is the similarity between a Structure, Union and enumeration?

40. Can a Structure contain a Pointer to itself?

41. How can we check whether the contents of two structure variables are same or not?

42. How are Structure passing and returning implemented by the complier?

43. How can we read/write Structures from/to data files?

44. What is the difference between an enumeration and a set of pre-processor # defines?

45. What do the ‘c’ and ‘v’ in argc and argv stand for?

46. Are the variables argc and argv are local to main?

47. What is the maximum combined length of command line arguments including the space between adjacent arguments?

48. If we want that any wildcard characters in the command line arguments should be appropriately expanded, are we required to make any special provision? If yes, which?

49. Does there exist any way to make the command line arguments available to other functions without passing them as arguments to the function?

50. What are bit fields? What is the use of bit fields in a Structure declaration?

51. To which numbering system can the binary number 1101100100111100 be easily converted to?

52. Which bit wise operator is suitable for checking whether a particular bit is on or off?

53. Which bit wise operator is suitable for turning off a particular bit in a number?

54. Which bit wise operator is suitable for putting on a particular bit in a number?

55. Which bit wise operator is suitable for checking whether a particular bit is on or off?

56. Which one is equivalent to multiplying by 2?

§ Left shifting a number by 1

§ Left shifting an unsigned int or char by 1?

57. Write a program to compare two strings without using the strcmp() function.

58. Write a program to concatenate two strings.

59. Write a program to interchange 2 variables without using the third one.

60. Write programs for String Reversal. The same for Palindrome check.

61. Write a program to find the Factorial of a number.

62. Write a program to generate the Fibonacci Series?

63. Write a program which employs Recursion?

64. Write a program which uses command line arguments.

65. Write a program which uses functions like strcmp(), strcpy(), etc.

66. What are the advantages of using typedef in a program?

67. How would you dynamically allocate a one-dimensional and two-dimensional array of integers?

68. How can you increase the size of a dynamically allocated array?

69. How can you increase the size of a statically allocated array?

70. When reallocating memory if any other pointers point into the same piece of memory do you have to readjust these other pointers or do they get readjusted automatically?

71. Which function should be used to free the memory allocated by calloc()?

72. How much maximum can you allocate in a single call to malloc()?

73. Can you dynamically allocate arrays in expanded memory?

74. What is object file? How can you access object file?

75. Which header file should you include if you are to develop a function which can accept variable number of arguments?

76. Can you write a function similar to printf()?

77. How can a called function determine the number of arguments that have been passed to it?

78. Can there be at least some solution to determine the number of arguments passed to a variable argument list function?

79. How do you declare the following:

§ An array of three pointers to chars

§ An array of three char pointers

§ A pointer to array of three chars

§ A pointer to function which receives an int pointer and returns a float pointer

§ A pointer to a function which receives nothing and returns nothing

80. What do the functions atoi(), itoa() and gcvt() do?

81. Does there exist any other function which can be used to convert an integer or a float to a string?

82. How would you use qsort() function to sort an array of structures?

83. How would you use qsort() function to sort the name stored in an array of pointers to string?

84. How would you use bsearch() function to search a name stored in array of pointers to string?

85. How would you use the functions sin(), pow(), sqrt()?

86. How would you use the functions memcpy(), memset(), memmove()?

87. How would you use the functions fseek(), freed(), fwrite() and ftell()?

88. How would you obtain the current time and difference between two times?

89. How would you use the functions randomize() and random()?

90. How would you implement a substr() function that extracts a sub string from a given string?

91. What is the difference between the functions rand(), random(), srand() and randomize()?

92. What is the difference between the functions memmove() and memcpy()?

93. How do you print a string on the printer?

94. Can you use the function fprintf() to display the output on the screen?

95. Gautam Pagedar adds this question: What is a linklist and why do we use it when we have arrays? - I feel the correct answer should be linklist is used in cases where you donÃ¢â‚¬â„¢t know the memory required to store a data structure and need to allocate is dynamically on demand.

96. How do you detect a loop in linked list?

97. Sunil asks: What is the difference between main() in C and main() in C++?

98. ajz at his interviews asks what will be printed out when the following code is executed:

Finding the nth highest salary of an employee.

2012-11-16T22:28:00.005-08:00

Create a table named Employee_Test and insert some test data as:-

CREATE TABLE Employee_Test
(
Emp_ID INT Identity,
Emp_name Varchar(100),
Emp_Sal Decimal (10,2)
)

INSERT INTO Employee_Test VALUES ('Anees',1000);
INSERT INTO Employee_Test VALUES ('Rick',1200);
INSERT INTO Employee_Test VALUES ('John',1100);
INSERT INTO Employee_Test VALUES ('Stephen',1300);
INSERT INTO Employee_Test VALUES ('Maria',1400);

It is very easy to find the highest salary as:-

--Highest Salary
select max(Emp_Sal) from Employee_Test

Now, if you are asked to find the 3rd highest salary, then the query is as:-

--3rd Highest Salary
select min(Emp_Sal) from Employee_Test where Emp_Sal in
(select distinct top 3 Emp_Sal from Employee_Test order by Emp_Sal desc)

The result is as :- 1200
To find the nth highest salary, replace the top 3 with top n (n being an integer 1,2,3 etc.)

--nth Highest Salary
select min(Emp_Sal) from Employee_Test where Emp_Sal in
(select distinct top n Emp_Sal from Employee_Test order by Emp_Sal desc)

Sql Interview - 2

2012-11-16T22:01:00.001-08:00

What is the difference between a "where" clause and a "having" clause? - "Where" is a kind of restiriction statement. You use where clause to restrict all the data from DB.Where clause is using before result retrieving. But Having clause is using after retrieving the data.Having clause is a kind of filtering command.
What is the basic form of a SQL statement to read data out of a table? The basic form to read data out of table is ‘SELECT * FROM table_name; ‘ An answer: ‘SELECT * FROM table_name WHERE xyz= ‘whatever’;’ cannot be called basic form because of WHERE clause.
What is a "join"? - ‘join’ used to connect two or more tables logically with or without common field.
What structure can you implement for the database to speed up table reads?- Follow the rules of DB tuning we have to: 1] properly use indexes ( different types of indexes) 2] properly locate different DB objects across different tablespaces, files and so on.3] create a special space (tablespace) to locate some of the data with special datatype ( for example CLOB, LOB and …)
What is "normalization"? "Denormalization"? Why do you sometimes want to denormalize? - Normalizing data means eliminating redundant information from a table and organizing the data so that future changes to the table are easier. Denormalization means allowing redundancy in a table. The main benefit of denormalization is improved performance with simplified data retrieval and manipulation. This is done by reduction in the number of joins needed for data processing.

Software Testing

2012-11-06T21:42:00.001-08:00

Software Testing
an activity to check whether the actual results match the expected results and to ensure that the software system is defect free.
Testing is important because software bugs could be expensive or even dangerous

Click Here For Briefly Know about Software Testing

The English Tense System

2012-11-06T04:19:00.002-08:00

Present Tense
I do do, I do
Present Continuous Tense
I am doing, I am doing tomorrow
Present Perfect Tense
I have done
Present Perfect Continuous Tense
I have been doing
Past Tense
I did do, I did
Past Continuous Tense
I was doing
Past Perfect Tense
I had done
Past Perfect Continuous Tense
I had been doing
Future Tense
I will do
Future Continuous Tense
I will be doing
Future Perfect Tense
I will have done
Future Perfect Continuous Tense
I will have been doing

Noun: a word that refers to a person, place, thing, event, substance or quality e.g.'nurse', 'cat', 'party', 'oil' and 'poverty'.
Verb: a word or phrase that describes an action, condition or experience e.g. 'run', 'look' and 'feel'.
Adjective: a word that describes a noun e.g. 'big', 'boring', 'pink', 'quick' and 'obvious'.

For More Details http://www.shabdkosh.com/
http://www.ecenglish.com/

Common search engine principles

2012-11-05T01:04:00.000-08:00

Spider - a browser-like program that downloads web pages.
Crawler – a program that automatically follows all of the links on each web page.
Indexer - a program that analyzes web pages downloaded by the spider and the crawler.
Database– storage for downloaded and processed pages.
Results engine – extracts search results from the database.
Web server – a server that is responsible for interaction between the user and other
search engine components

In Breif-------
Spider. This program downloads web pages just like a web browser. The difference is that a browser displays the information presented on each page (text, graphics, etc.) while a spider does not have any visual components and works directly with the underlying HTML code of the page. You may already know that there is an option in standard web browsers to view source HTML code.

Crawler. This program finds all links on each page. Its task is to determine where the spider should go either by evaluating the links or according to a predefined list of addresses. The crawler follows these links and tries to find documents not already known
to the search engine.

Indexer. This component parses each page and analyzes the various elements, such as text, headers, structural or stylistic features, special HTML tags, etc.

Database. This is the storage area for the data that the search engine downloads and analyzes. Sometimes it is called the index of the search engine.Results Engine.

The results engine ranks pages. It determines which pages best match a user's query and in what order the pages should be listed. This is done according to the ranking algorithms of the search engine. It follows that page rank is a valuable and interesting property and any seo specialist is most interested in it when trying to improve his site search results. In this article, we will discuss the seo factors that influence page rank in some detail.

Web server. The search engine web server usually contains a HTML page with an input field where the user can specify the search query he or she is interested in. The web server is also responsible for displaying search results to the user in the form of an HTML page.

Computer Network

2012-11-04T23:31:00.004-08:00

What is a computer Network?

A network is any collection of independent computers that communicate with one another over a shared network medium. A computer network is a collection of two or more connected computers. When these computers are joined in a network, people can share files and peripherals such as modems, printers, tape backup drives, or CD-ROM drives. When networks at multiple locations are connected using services available from phone companies, people can send e-mail, share links to the global Internet, or conduct video conferences in real time with other remote users. When a network becomes open sourced it can be managed properly with online collaboration software. As companies rely on applications like electronic mail and database management for core business operations, computer networking becomes increasingly more important.

Every network includes:

· At least two computers Server or Client workstation.

· Networking Interface Card's (NIC)

· A connection medium, usually a wire or cable, although wireless communication between networked computers and peripherals is also possible.

· Network Operating system software, such as Microsoft Windows NT or 2000, Novell NetWare, Unix and Linux.

Types of Networks:

LANs (Local Area Networks)

A network is any collection of independent computers that communicate with one another over a shared network medium. LANs are networks usually confined to a geographic area, such as a single building or a college campus. LANs can be small, linking as few as three computers, but often link hundreds of computers used by thousands of people. The development of standard networking protocols and media has resulted in worldwide proliferation of LANs throughout business and educational organizations.

WANs (Wide Area Networks)

Wide area networking combines multiple LANs that are geographically separate. This is accomplished by connecting the different LANs using services such as dedicated leased phone lines, dial-up phone lines (both synchronous and asynchronous), satellite links, and data packet carrier services. Wide area networking can be as simple as a modem and remote access server for employees to dial into, or it can be as complex as hundreds of branch offices globally linked using special routing protocols and filters to minimize the expense of sending data sent over vast distances.

Internet

The Internet is a system of linked networks that are worldwide in scope and facilitate data communication services such as remote login, file transfer, electronic mail, the World Wide Web and newsgroups.

With the meteoric rise in demand for connectivity, the Internet has become a communications highway for millions of users. The Internet was initially restricted to military and academic institutions, but now it is a full-fledged conduit for any and all forms of information and commerce. Internet websites now provide personal, educational, political and economic resources to every corner of the planet.

Intranet

With the advancements made in browser-based software for the Internet, many private organizations are implementing intranets. An intranet is a private network utilizing Internet-type tools, but available only within that organization. For large organizations, an intranet provides an easy access mode to corporate information for employees.

MANs (Metropolitan area Networks)

The refers to a network of computers with in a City.

VPN (Virtual Private Network)

VPN uses a technique known as tunneling to transfer data securely on the Internet to a remote access server on your workplace network. Using a VPN helps you save money by using the public Internet instead of making long–distance phone calls to connect securely with your private network. There are two ways to create a VPN connection, by dialing an Internet service provider (ISP), or connecting directly to Internet.

Categories of Network:

Network can be divided in to two main categories:

Peer-to-peer.
Server – based.

In peer-to-peer networking there are no dedicated servers or hierarchy among the computers. All of the computers are equal and therefore known as peers. Normally each computer serves as Client/Server and there is no one assigned to be an administrator responsible for the entire network.

Peer-to-peer networks are good choices for needs of small organizations where the users are allocated in the same general area, security is not an issue and the organization and the network will have limited growth within the foreseeable future.

The term Client/server refers to the concept of sharing the work involved in processing data between the client computer and the most powerful server computer.

The client/server network is the most efficient way to provide:

Databases and management of applications such as Spreadsheets, Accounting, Communications and Document management.
Network management.
Centralized file storage.

The client/server model is basically an implementation of distributed or cooperative processing. At the heart of the model is the concept of splitting application functions between a client and a server processor. The division of labor between the different processors enables the application designer to place an application function on the processor that is most appropriate for that function. This lets the software designer optimize the use of processors--providing the greatest possible return on investment for the hardware.

Client/server application design also lets the application provider mask the actual location of application function. The user often does not know where a specific operation is executing. The entire function may execute in either the PC or server, or the function may be split between them. This masking of application function locations enables system implementers to upgrade portions of a system over time with a minimum disruption of application operations, while protecting the investment in existing hardware and software.

The OSI Model:

Open System Interconnection (OSI) reference model has become an International standard and serves as a guide for networking. This model is the best known and most widely used guide to describe networking environments. Vendors design network products based on the specifications of the OSI model. It provides a description of how network hardware and software work together in a layered fashion to make communications possible. It also helps with trouble shooting by providing a frame of reference that describes how components are supposed to function.

There are seven to get familiar with and these are the physical layer, data link layer, network layer, transport layer, session layer, presentation layer, and the application layer.

Physical Layer, is just that the physical parts of the network such as wires, cables, and there media along with the length. Also this layer takes note of the electrical signals that transmit data throughout system.
Data Link Layer, this layer is where we actually assign meaning to the electrical signals in the network. The layer also determines the size and format of data sent to printers, and other devices. Also I don't want to forget that these are also called nodes in the network. Another thing to consider in this layer is will also allow and define the error detection and correction schemes that insure data was sent and received.
Network Layer, this layer provides the definition for the connection of two dissimilar networks.
Transport Layer, this layer allows data to be broken into smaller packages for data to be distributed and addressed to other nodes (workstations).
Session Layer, this layer helps out with the task to carry information from one node (workstation) to another node (workstation). A session has to be made before we can transport information to another computer.
Presentation Layer, this layer is responsible to code and decode data sent to the node.
Application Layer, this layer allows you to use an application that will communicate with say the operation system of a server. A good example would be using your web browser to interact with the operating system on a server such as Windows NT, which in turn gets the data you requested.

Network Architectures:

Ethernet

Ethernet is the most popular physical layer LAN technology in use today. Other LAN types include Token Ring, Fast Ethernet, Fiber Distributed Data Interface (FDDI), Asynchronous Transfer Mode (ATM) and LocalTalk. Ethernet connection is popular because it strikes a good balance between speed, cost and ease of installation. These benefits, combined with wide acceptance in the computer marketplace and the ability to support virtually all popular network protocols, make Ethernet an ideal networking technology for most computer users today. The Institute for Electrical and Electronic Engineers (IEEE) defines the Ethernet standard as IEEE Standard 802.3. This standard defines rules for configuring an Ethernet network as well as specifying how elements in an Ethernet network interact with one another. By adhering to the IEEE standard, network equipment and network protocols can communicate efficiently.

Fast Ethernet

For Ethernet networks that need higher transmission speeds, the Fast Ethernet standard (IEEE 802.3u) has been established. This standard raises the Ethernet speed limit from 10 Megabits per second (Mbps) to 100 Mbps with only minimal changes to the existing cable structure. There are three types of Fast Ethernet: 100BASE-TX for use with level 5 UTP cable, 100BASE-FX for use with fiber-optic cable, and 100BASE-T4 which utilizes an extra two wires for use with level 3 UTP cable. The 100BASE-TX standard has become the most popular due to its close compatibility with the 10BASE-T Ethernet standard. For the network manager, the incorporation of Fast Ethernet into an existing configuration presents a host of decisions. Managers must determine the number of users in each site on the network that need the higher throughput, decide which segments of the backbone need to be reconfigured specifically for 100BASE-T and then choose the necessary hardware to connect the 100BASE-T segments with existing 10BASE-T segments. Gigabit Ethernet is a future technology that promises a migration path beyond Fast Ethernet so the next generation of networks will support even higher data transfer speeds.

Token Ring

Token Ring is another form of network configuration which differs from Ethernet in that all messages are transferred in a unidirectional manner along the ring at all times. Data is transmitted in tokens, which are passed along the ring and viewed by each device. When a device sees a message addressed to it, that device copies the message and then marks that message as being read. As the message makes its way along the ring, it eventually gets back to the sender who now notes that the message was received by the intended device. The sender can then remove the message and free that token for use by others.

Various PC vendors have been proponents of Token Ring networks at different times and thus these types of networks have been implemented in many organizations.

FDDI

FDDI (Fiber-Distributed Data Interface) is a standard for data transmission on fiber optic lines in a local area network that can extend in range up to 200 km (124 miles). The FDDI protocol is based on the token ring protocol. In addition to being large geographically, an FDDI local area network can support thousands of users.

Protocols:

Network protocols are standards that allow computers to communicate. A protocol defines how computers identify one another on a network, the form that the data should take in transit, and how this information is processed once it reaches its final destination. Protocols also define procedures for handling lost or damaged transmissions or "packets." TCP/IP (for UNIX, Windows NT, Windows 95 and other platforms), IPX (for Novell NetWare), DECnet (for networking Digital Equipment Corp. computers), AppleTalk (for Macintosh computers), and NetBIOS/NetBEUI (for LAN Manager and Windows NT networks) are the main types of network protocols in use today.

Although each network protocol is different, they all share the same physical cabling. This common method of accessing the physical network allows multiple protocols to peacefully coexist over the network media, and allows the builder of a network to use common hardware for a variety of protocols. This concept is known as "protocol independence,"

Some Important Protocols and their job:

Protocol	Acronym	Its Job
Point-To-Point	TCP/IP	The backbone protocol of the internet. Popular also for intranets using the internet
Transmission Control Protocol/internet Protocol	TCP/IP	The backbone protocol of the internet. Popular also for intranets using the internet
Internetwork Package Exchange/Sequenced Packet Exchange	IPX/SPX	This is a standard protocol for Novell Network Operating System
NetBIOS Extended User Interface	NetBEUI	This is a Microsoft protocol that doesn't support routing to other networks
File Transfer Protocol	FTP	Used to send and receive files from a remote host
Hyper Text Transfer Protocol	HTTP	Used for the web to send documents that are encoded in HTML.
Network File Services	NFS	Allows network nodes or workstations to access files and drives as if they were their own.
Simple Mail Transfer Protocol	SMTP	Used to send Email over a network
Telnet		Used to connect to a host and emulate a terminal that the remote server can recognize

Introduction to TCP/IP Networks:

TCP/IP-based networks play an increasingly important role in computer networks. Perhaps one reason for their appeal is that they are based on an open specification that is not controlled by any vendor.

What Is TCP/IP?

TCP stands for Transmission Control Protocol and IP stands for Internet Protocol. The term TCP/IP is not limited just to these two protocols, however. Frequently, the term TCP/IP is used to refer to a group of protocols related to the TCP and IP protocols such as the User Datagram Protocol (UDP), File Transfer Protocol (FTP), Terminal Emulation Protocol (TELNET), and so on.

The Origins of TCP/IP

In the late 1960s, DARPA (the Defense Advanced Research Project Agency), in the United States, noticed that there was a rapid proliferation of computers in military communications. Computers, because they can be easily programmed, provide flexibility in achieving network functions that is not available with other types of communications equipment. The computers then used in military communications were manufactured by different vendors and were designed to interoperate with computers from that vendor only. Vendors used proprietary protocols in their communications equipment. The military had a multi vendor network but no common protocol to support the heterogeneous equipment from different vendors

Net work Cables and Stuff:

In the network you will commonly find three types of cables used these are the, coaxial cable, fiber optic and twisted pair.

Thick Coaxial Cable

This type cable is usually yellow in color and used in what is called thicknets, and has two conductors. This coax can be used in 500-meter lengths. The cable itself is made up of a solid center wire with a braided metal shield and plastic sheathing protecting the rest of the wire.

Thin Coaxial Cable

As with the thick coaxial cable is used in thicknets the thin version is used in thinnets. This type cable is also used called or referred to as RG-58. The cable is really just a cheaper version of the thick cable.

Fiber Optic Cable

As we all know fiber optics are pretty darn cool and not cheap. This cable is smaller and can carry a vast amount of information fast and over long distances.

Twisted Pair Cables

These come in two flavors of unshielded and shielded.

Shielded Twisted Pair (STP)

Is more common in high-speed networks. The biggest difference you will see in the UTP and STP is that the STP use's metallic shield wrapping to protect the wire from interference.

-Something else to note about these cables is that they are defined in numbers also. The bigger the number the better the protection from interference. Most networks should go with no less than a CAT 3 and CAT 5 is most recommended.

-Now you know about cables we need to know about connectors. This is pretty important and you will most likely need the RJ-45 connector. This is the cousin of the phone jack connector and looks real similar with the exception that the RJ-45 is bigger. Most commonly your connector are in two flavors and this is BNC (Bayonet Naur Connector) used in thicknets and the RJ-45 used in smaller networks using UTP/STP.

Unshielded Twisted Pair (UTP)

This is the most popular form of cables in the network and the cheapest form that you can go with. The UTP has four pairs of wires and all inside plastic sheathing. The biggest reason that we call it Twisted Pair is to protect the wires from interference from themselves. Each wire is only protected with a thin plastic sheath.

Ethernet Cabling

Now to familiarize you with more on the Ethernet and it's cabling we need to look at the 10's. 10Base2, is considered the thin Ethernet, thinnet, and thinwire which uses light coaxial cable to create a 10 Mbps network. The cable segments in this network can't be over 185 meters in length. These cables connect with the BNC connector. Also as a note these unused connection must have a terminator, which will be a 50-ohm terminator.

10Base5, this is considered a thicknet and is used with coaxial cable arrangement such as the BNC connector. The good side to the coaxial cable is the high-speed transfer and cable segments can be up to 500 meters between nodes/workstations. You will typically see the same speed as the 10Base2 but larger cable lengths for more versatility.

10BaseT, the “T” stands for twisted as in UTP (Unshielded Twisted Pair) and uses this for 10Mbps of transfer. The down side to this is you can only have cable lengths of 100 meters between nodes/workstations. The good side to this network is they are easy to set up and cheap! This is why they are so common an ideal for small offices or homes.

100BaseT, is considered Fast Ethernet uses STP (Shielded Twisted Pair) reaching data transfer of 100Mbps. This system is a little more expensive but still remains popular as the 10BaseT and cheaper than most other type networks. This on of course would be the cheap fast version.

10BaseF, this little guy has the advantage of fiber optics and the F stands for just that. This arrangement is a little more complicated and uses special connectors and NIC's along with hubs to create its network. Pretty darn neat and not to cheap on the wallet.

An important part of designing and installing an Ethernet is selecting the appropriate Ethernet medium. There are four major types of media in use today: Thickwire for 10BASE5 networks, thin coax for 10BASE2 networks, unshielded twisted pair (UTP) for 10BASE-T networks and fiber optic for 10BASE-FL or Fiber-Optic Inter-Repeater Link (FOIRL) networks. This wide variety of media reflects the evolution of Ethernet and also points to the technology's flexibility. Thickwire was one of the first cabling systems used in Ethernet but was expensive and difficult to use. This evolved to thin coax, which is easier to work with and less expensive.

Network Topologies:

What is a Network topology?

A network topology is the geometric arrangement of nodes and cable links in a LAN,

There are three topology's to think about when you get into networks. These are the star, rind, and the bus.

Star, in a star topology each node has a dedicated set of wires connecting it to a central network hub. Since all traffic passes through the hub, the hub becomes a central point for isolating network problems and gathering network statistics.

Ring, a ring topology features a logically closed loop. Data packets travel in a single direction around the ring from one network device to the next. Each network device acts as a repeater, meaning it regenerates the signal

Bus, the bus topology, each node (computer, server, peripheral etc.) attaches directly to a common cable. This topology most often serves as the backbone for a network. In some instances, such as in classrooms or labs, a bus will connect small workgroups

Collisions:

Ethernet is a shared media, so there are rules for sending packets of data to avoid conflicts and protect data integrity. Nodes determine when the network is available for sending packets. It is possible that two nodes at different locations attempt to send data at the same time. When both PCs are transferring a packet to the network at the same time, a collision will result.

Minimizing collisions is a crucial element in the design and operation of networks. Increased collisions are often the result of too many users on the network, which results in a lot of contention for network bandwidth. This can slow the performance of the network from the user's point of view. Segmenting the network, where a network is divided into different pieces joined together logically with a bridge or switch, is one way of reducing an overcrowded network.

Ethernet Products:

The standards and technology that have just been discussed help define the specific products that network managers use to build Ethernet networks. The following text discusses the key products needed to build an Ethernet LAN.

Transceivers

Transceivers are used to connect nodes to the various Ethernet media. Most computers and network interface cards contain a built-in 10BASE-T or 10BASE2 transceiver, allowing them to be connected directly to Ethernet without requiring an external transceiver. Many Ethernet devices provide an AUI connector to allow the user to connect to any media type via an external transceiver. The AUI connector consists of a 15-pin D-shell type connector, female on the computer side, male on the transceiver side. Thickwire (10BASE5) cables also use transceivers to allow connections.

For Fast Ethernet networks, a new interface called the MII (Media Independent Interface) was developed to offer a flexible way to support 100 Mbps connections. The MII is a popular way to connect 100BASE-FX links to copper-based Fast Ethernet devices.

Network Interface Cards:

Network interface cards, commonly referred to as NICs, and are used to connect a PC to a network. The NIC provides a physical connection between the networking cable and the computer's internal bus. Different computers have different bus architectures; PCI bus master slots are most commonly found on 486/Pentium PCs and ISA expansion slots are commonly found on 386 and older PCs. NICs come in three basic varieties: 8-bit, 16-bit, and 32-bit. The larger the number of bits that can be transferred to the NIC, the faster the NIC can transfer data to the network cable.

Many NIC adapters comply with Plug-n-Play specifications. On these systems, NICs are automatically configured without user intervention, while on non-Plug-n-Play systems, configuration is done manually through a setup program and/or DIP switches.

Cards are available to support almost all networking standards, including the latest Fast Ethernet environment. Fast Ethernet NICs are often 10/100 capable, and will automatically set to the appropriate speed. Full duplex networking is another option, where a dedicated connection to a switch allows a NIC to operate at twice the speed.

Hubs/Repeaters:

Hubs/repeaters are used to connect together two or more Ethernet segments of any media type. In larger designs, signal quality begins to deteriorate as segments exceed their maximum length. Hubs provide the signal amplification required to allow a segment to be extended a greater distance. A hub takes any incoming signal and repeats it out all ports.

Ethernet hubs are necessary in star topologies such as 10BASE-T. A multi-port twisted pair hub allows several point-to-point segments to be joined into one network. One end of the point-to-point link is attached to the hub and the other is attached to the computer. If the hub is attached to a backbone, then all computers at the end of the twisted pair segments can communicate with all the hosts on the backbone. The number and type of hubs in any one-collision domain is limited by the Ethernet rules. These repeater rules are discussed in more detail later.

Network Type	Max Nodes Per Segment	Max Distance Per Segment
10BASE-T 10BASE2 10BASE5 10BASE-FL	2 30 100 2	100m 185m 500m 2000m

Adding Speed:

While repeaters allow LANs to extend beyond normal distance limitations, they still limit the number of nodes that can be supported. Bridges and switches, however, allow LANs to grow significantly larger by virtue of their ability to support full Ethernet segments on each port. Additionally, bridges and switches selectively filter network traffic to only those packets needed on each segment - this significantly increases throughput on each segment and on the overall network. By providing better performance and more flexibility for network topologies, bridges and switches will continue to gain popularity among network managers.

Bridges:

The function of a bridge is to connect separate networks together. Bridges connect different networks types (such as Ethernet and Fast Ethernet) or networks of the same type. Bridges map the Ethernet addresses of the nodes residing on each network segment and allow only necessary traffic to pass through the bridge. When a packet is received by the bridge, the bridge determines the destination and source segments. If the segments are the same, the packet is dropped ("filtered"); if the segments are different, then the packet is "forwarded" to the correct segment. Additionally, bridges do not forward bad or misaligned packets.

Bridges are also called "store-and-forward" devices because they look at the whole Ethernet packet before making filtering or forwarding decisions. Filtering packets, and regenerating forwarded packets enable bridging technology to split a network into separate collision domains. This allows for greater distances and more repeaters to be used in the total network design.

Ethernet Switches:

Ethernet switches are an expansion of the concept in Ethernet bridging. LAN switches can link four, six, ten or more networks together, and have two basic architectures: cut-through and store-and-forward. In the past, cut-through switches were faster because they examined the packet destination address only before forwarding it on to its destination segment. A store-and-forward switch, on the other hand, accepts and analyzes the entire packet before forwarding it to its destination.

It takes more time to examine the entire packet, but it allows the switch to catch certain packet errors and keep them from propagating through the network. Both cut-through and store-and-forward switches separate a network into collision domains, allowing network design rules to be extended. Each of the segments attached to an Ethernet switch has a full 10 Mbps of bandwidth shared by fewer users, which results in better performance (as opposed to hubs that only allow bandwidth sharing from a single Ethernet). Newer switches today offer high-speed links, FDDI, Fast Ethernet or ATM. These are used to link switches together or give added bandwidth to high-traffic servers. A network composed of a number of switches linked together via uplinks is termed a "collapsed backbone" network.

Routers:

Routers filter out network traffic by specific protocol rather than by packet address. Routers also divide networks logically instead of physically. An IP router can divide a network into various subnets so that only traffic destined for particular IP addresses can pass between segments. Network speed often decreases due to this type of intelligent forwarding. Such filtering takes more time than that exercised in a switch or bridge, which only looks at the Ethernet address. However, in more complex networks, overall efficiency is improved by using routers.

What is a network firewall?

A firewall is a system or group of systems that enforces an access control policy between two networks. The actual means by which this is accomplished varies widely, but in principle, the firewall can be thought of as a pair of mechanisms: one which exists to block traffic, and the other which exists to permit traffic. Some firewalls place a greater emphasis on blocking traffic, while others emphasize permitting traffic. Probably the most important thing to recognize about a firewall is that it implements an access control policy. If you don't have a good idea of what kind of access you want to allow or to deny, a firewall really won't help you. It's also important to recognize that the firewall's configuration, because it is a mechanism for enforcing policy, imposes its policy on everything behind it. Administrators for firewalls managing the connectivity for a large number of hosts therefore have a heavy responsibility.

Network Design Criteria:

Ethernets and Fast Ethernets have design rules that must be followed in order to function correctly. Maximum number of nodes, number of repeaters and maximum segment distances are defined by the electrical and mechanical design properties of each type of Ethernet and Fast Ethernet media.

A network using repeaters, for instance, functions with the timing constraints of Ethernet. Although electrical signals on the Ethernet media travel near the speed of light, it still takes a finite time for the signal to travel from one end of a large Ethernet to another. The Ethernet standard assumes it will take roughly 50 microseconds for a signal to reach its destination.

Ethernet is subject to the "5-4-3" rule of repeater placement: the network can only have five segments connected; it can only use four repeaters; and of the five segments, only three can have users attached to them; the other two must be inter-repeater links.

If the design of the network violates these repeater and placement rules, then timing guidelines will not be met and the sending station will resend that packet. This can lead to lost packets and excessive resent packets, which can slow network performance and create trouble for applications. Fast Ethernet has modified repeater rules, since the minimum packet size takes less time to transmit than regular Ethernet. The length of the network links allows for a fewer number of repeaters. In Fast Ethernet networks, there are two classes of repeaters. Class I repeaters have a latency of 0.7 microseconds or less and are limited to one repeater per network. Class II repeaters have a latency of 0.46 microseconds or less and are limited to two repeaters per network. The following are the distance (diameter) characteristics for these types of Fast Ethernet repeater combinations:

Fast Ethernet	Copper	Fiber
No Repeaters One Class I Repeater One Class II Repeater Two Class II Repeaters	100m 200m 200m 205m	412m* 272m 272m 228m

* Full Duplex Mode 2 km

When conditions require greater distances or an increase in the number of nodes/repeaters, then a bridge, router or switch can be used to connect multiple networks together. These devices join two or more separate networks, allowing network design criteria to be restored. Switches allow network designers to build large networks that function well. The reduction in costs of bridges and switches reduces the impact of repeater rules on network design.

Each network connected via one of these devices is referred to as a separate collision domain in the overall network.

Types of Servers:

Device Servers

A device server is defined as a specialized, network-based hardware device designed to perform a single or specialized set of server functions. It is characterized by a minimal operating architecture that requires no per seat network operating system license, and client access that is independent of any operating system or proprietary protocol. In addition the device server is a "closed box," delivering extreme ease of installation, minimal maintenance, and can be managed by the client remotely via a Web browser.

Print servers, terminal servers, remote access servers and network time servers are examples of device servers which are specialized for particular functions. Each of these types of servers has unique configuration attributes in hardware or software that help them to perform best in their particular arena.

Print Servers

Print servers allow printers to be shared by other users on the network. Supporting either parallel and/or serial interfaces, a print server accepts print jobs from any person on the network using supported protocols and manages those jobs on each appropriate printer.

Print servers generally do not contain a large amount of memory; printers simply store information in a queue. When the desired printer becomes available, they allow the host to transmit the data to the appropriate printer port on the server. The print server can then simply queue and print each job in the order in which print requests are received, regardless of protocol used or the size of the job.

Multiport Device Servers

Devices that are attached to a network through a multiport device server can be shared between terminals and hosts at both the local site and throughout the network. A single terminal may be connected to several hosts at the same time (in multiple concurrent sessions), and can switch between them. Multiport device servers are also used to network devices that have only serial outputs. A connection between serial ports on different servers is opened, allowing data to move between the two devices.

Given its natural translation ability, a multi-protocol multiport device server can perform conversions between the protocols it knows, like LAT and TCP/IP. While server bandwidth is not adequate for large file transfers, it can easily handle host-to-host inquiry/response applications, electronic mailbox checking, etc. And it is far more economical than the alternatives of acquiring expensive host software and special-purpose converters. Multiport device and print servers give their users greater flexibility in configuring and managing their networks.

Whether it is moving printers and other peripherals from one network to another, expanding the dimensions of interoperability or preparing for growth, multiport device servers can fulfill your needs, all without major rewiring.

Access Servers

While Ethernet is limited to a geographic area, remote users such as traveling sales people need access to network-based resources. Remote LAN access, or remote access, is a popular way to provide this connectivity. Access servers use telephone services to link a user or office with an office network. Dial-up remote access solutions such as ISDN or asynchronous dial introduce more flexibility. Dial-up remote access offers both the remote office and the remote user the economy and flexibility of "pay as you go" telephone services. ISDN is a special telephone service that offers three channels, two 64 Kbps "B" channels for user data and a "D" channel for setting up the connection. With ISDN, the B channels can be combined for double bandwidth or separated for different applications or users. With asynchronous remote access, regular telephone lines are combined with modems and remote access servers to allow users and networks to dial anywhere in the world and have data access. Remote access servers provide connection points for both dial-in and dial-out applications on the network to which they are attached. These hybrid devices route and filter protocols and offer other services such as modem pooling and terminal/printer services. For the remote PC user, one can connect from any available telephone jack (RJ45), including those in a hotel rooms or on most airplanes.

Network Time Servers

A network time server is a server specialized in the handling of timing information from sources such as satellites or radio broadcasts and is capable of providing this timing data to its attached network. Specialized protocols such as NTP or udp/time allow a time server to communicate to other network nodes ensuring that activities that must be coordinated according to their time of execution are synchronized correctly. GPS satellites are one source of information that can allow global installations to achieve constant timing.

IP Addressing:

An IP (Internet Protocol) address is a unique identifier for a node or host connection on an IP network. An IP address is a 32 bit binary number usually represented as 4 decimal values, each representing 8 bits, in the range 0 to 255 (known as octets) separated by decimal points. This is known as "dotted decimal" notation.

Example: 140.179.220.200

It is sometimes useful to view the values in their binary form.

140 .179 .220 .200

10001100.10110011.11011100.11001000

Every IP address consists of two parts, one identifying the network and one identifying the node. The Class of the address and the subnet mask determine which part belongs to the network address and which part belongs to the node address.

Address Classes:

There are 5 different address classes. You can determine which class any IP address is in by examining the first 4 bits of the IP address.

Class A addresses begin with 0xxx, or 1 to 126 decimal.

Class B addresses begin with 10xx, or 128 to 191 decimal.

Class C addresses begin with 110x, or 192 to 223 decimal.

Class D addresses begin with 1110, or 224 to 239 decimal.

Class E addresses begin with 1111, or 240 to 254 decimal.

Addresses beginning with 01111111, or 127 decimal, are reserved for loopback and for internal testing on a local machine. [You can test this: you should always be able to ping 127.0.0.1, which points to yourself] Class D addresses are reserved for multicasting. Class E addresses are reserved for future use. They should not be used for host addresses.

Now we can see how the Class determines, by default, which part of the IP address belongs to the network (N) and which part belongs to the node (n).

Class A -- NNNNNNNN.nnnnnnnn.nnnnnnn.nnnnnnn

Class B -- NNNNNNNN.NNNNNNNN.nnnnnnnn.nnnnnnnn

Class C -- NNNNNNNN.NNNNNNNN.NNNNNNNN.nnnnnnnn

In the example, 140.179.220.200 is a Class B address so by default the Network part of the address (also known as the Network Address) is defined by the first two octets (140.179.x.x) and the node part is defined by the last 2 octets (x.x.220.200).

In order to specify the network address for a given IP address, the node section is set to all "0"s. In our example, 140.179.0.0 specifies the network address for 140.179.220.200. When the node section is set to all "1"s, it specifies a broadcast that is sent to all hosts on the network. 140.179.255.255 specifies the example broadcast address. Note that this is true regardless of the length of the node section.

Private Subnets:

There are three IP network addresses reserved for private networks. The addresses are 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16. They can be used by anyone setting up internal IP networks, such as a lab or home LAN behind a NAT or proxy server or a router. It is always safe to use these because routers on the Internet will never forward packets coming from these addresses

Subnetting an IP Network can be done for a variety of reasons, including organization, use of different physical media (such as Ethernet, FDDI, WAN, etc.), preservation of address space, and security. The most common reason is to control network traffic. In an Ethernet network, all nodes on a segment see all the packets transmitted by all the other nodes on that segment. Performance can be adversely affected under heavy traffic loads, due to collisions and the resulting retransmissions. A router is used to connect IP networks to minimize the amount of traffic each segment must receive.

Subnet Masking

Applying a subnet mask to an IP address allows you to identify the network and node parts of the address. The network bits are represented by the 1s in the mask, and the node bits are represented by the 0s. Performing a bitwise logical AND operation between the IP address and the subnet mask results in the Network Address or Number.

For example, using our test IP address and the default Class B subnet mask, we get:

10001100.10110011.11110000.11001000 140.179.240.200 Class B IP Address

11111111.11111111.00000000.00000000 255.255.000.000 Default Class B Subnet Mask

10001100.10110011.00000000.00000000 140.179.000.000 Network Address

Default subnet masks:

Class A - 255.0.0.0 - 11111111.00000000.00000000.00000000

Class B - 255.255.0.0 - 11111111.11111111.00000000.00000000

Class C - 255.255.255.0 - 11111111.11111111.11111111.00000000

CIDR -- Classless InterDomain Routing.

CIDR was invented several years ago to keep the internet from running out of IP addresses. The "classful" system of allocating IP addresses can be very wasteful; anyone who could reasonably show a need for more that 254 host addresses was given a Class B address block of 65533 host addresses. Even more wasteful were companies and organizations that were allocated Class A address blocks, which contain over 16 Million host addresses! Only a tiny percentage of the allocated Class A and Class B address space has ever been actually assigned to a host computer on the Internet.

People realized that addresses could be conserved if the class system was eliminated. By accurately allocating only the amount of address space that was actually needed, the address space crisis could be avoided for many years. This was first proposed in 1992 as a scheme called Supernetting.

The use of a CIDR notated address is the same as for a Classful address. Classful addresses can easily be written in CIDR notation (Class A = /8, Class B = /16, and Class C = /24)

It is currently almost impossible for an individual or company to be allocated their own IP address blocks. You will simply be told to get them from your ISP. The reason for this is the ever-growing size of the internet routing table. Just 5 years ago, there were less than 5000 network routes in the entire Internet. Today, there are over 90,000. Using CIDR, the biggest ISPs are allocated large chunks of address space (usually with a subnet mask of /19 or even smaller); the ISP's customers (often other, smaller ISPs) are then allocated networks from the big ISP's pool. That way, all the big ISP's customers (and their customers, and so on) are accessible via 1 network route on the Internet.

It is expected that CIDR will keep the Internet happily in IP addresses for the next few years at least. After that, IPv6, with 128 bit addresses, will be needed. Under IPv6, even sloppy address allocation would comfortably allow a billion unique IP addresses for every person on earth

Examining your network with commands:

PING is used to check for a response from another computer on the network. It can tell you a great deal of information about the status of the network and the computers you are communicating with.

Ping returns different responses depending on the computer in question. The responses are similar depending on the options used.

Ping uses IP to request a response from the host. It does not use TCP

.It takes its name from a submarine sonar search - you send a short sound burst and listen for an echo - a ping - coming back.

In an IP network, `ping' sends a short data burst - a single packet - and listens for a single packet in reply. Since this tests the most basic function of an IP network (delivery of single packet), it's easy to see how you can learn a lot from some `pings'.

To stop ping, type control-c. This terminates the program and prints out a nice summary of the number of packets transmitted, the number received, and the percentage of packets lost, plus the minimum, average, and maximum round-trip times of the packets.

Sample ping session

PING localhost (127.0.0.1): 56 data bytes
64 bytes from 127.0.0.1: icmp_seq=0 ttl=255 time=2 ms
64 bytes from 127.0.0.1: icmp_seq=1 ttl=255 time=2 ms
64 bytes from 127.0.0.1: icmp_seq=2 ttl=255 time=2 ms
64 bytes from 127.0.0.1: icmp_seq=3 ttl=255 time=2 ms
64 bytes from 127.0.0.1: icmp_seq=4 ttl=255 time=2 ms
64 bytes from 127.0.0.1: icmp_seq=5 ttl=255 time=2 ms
64 bytes from 127.0.0.1: icmp_seq=6 ttl=255 time=2 ms
64 bytes from 127.0.0.1: icmp_seq=7 ttl=255 time=2 ms
64 bytes from 127.0.0.1: icmp_seq=8 ttl=255 time=2 ms
64 bytes from 127.0.0.1: icmp_seq=9 ttl=255 time=2 ms

localhost ping statistics

10 packets transmitted, 10 packets received, 0% packet loss
round-trip min/avg/max = 2/2/2 ms
meikro$

The Time To Live (TTL) field can be interesting. The main purpose of this is so that a packet doesn't live forever on the network and will eventually die when it is deemed "lost." But for us, it provides additional information. We can use the TTL to determine approximately how many router hops the packet has gone through. In this case it's 255 minus N hops, where N is the TTL of the returning Echo Replies. If the TTL field varies in successive pings, it could indicate that the successive reply packets are going via different routes, which isn't a great thing.

The time field is an indication of the round-trip time to get a packet to the remote host. The reply is measured in milliseconds. In general, it's best if round-trip times are under 200 milliseconds. The time it takes a packet to reach its destination is called latency. If you see a large variance in the round-trip times (which is called "jitter"), you are going to see poor performance talking to the host

NSLOOKUP

NSLOOKUP is an application that facilitates looking up hostnames on the network. It can reveal the IP address of a host or, using the IP address, return the host name.

It is very important when troubleshooting problems on a network that you can verify the components of the networking process. Nslookup allows this by revealing details within the infrastructure.

NETSTAT

NETSTAT is used to look up the various active connections within a computer. It is helpful to understand what computers or networks you are connected to. This allows you to further investigate problems. One host may be responding well but another may be less responsive.

IPconfig

This is a Microsoft windows NT, 2000 command. It is very useful in determining what could be wrong with a network.

This command when used with the /all switch, reveal enormous amounts of troubleshooting information within the system.

Windows 2000 IP Configuration

Host Name . . . . . . . . . . . . : cowder
Primary DNS Suffix . . . . . . . :
Node Type . . . . . . . . . . . . : Broadcast
IP Routing Enabled. . . . . . . . : No
WINS Proxy Enabled. . . . . . . . : No
WINS Proxy Enabled. . . . . . . . : No
Connection-specific DNS Suffix . :
Description . . . . . . . . . . . :
WAN (PPP/SLIP) Interface
Physical Address. . . . . . . . . : 00-53-45-00-00-00
DHCP Enabled. . . . . . . . . . . : No
IP Address. . . . . . . . . . . . : 12.90.108.123
Subnet Mask . . . . . . . . . . . : 255.255.255.255
Default Gateway . . . . . . . . . : 12.90.108.125
DNS Servers . . . . . . . . . . . : 12.102.244.2
204.127.129.2

Traceroute

Traceroute on Unix and Linux (or tracert in the Microsoft world) attempts to trace the current network path to a destination. Here is an example of a traceroute run to www.berkeley.edu:

$ traceroute www.berkeley.edu

traceroute to amber.Berkeley.EDU (128.32.25.12), 30 hops max, 40 byte packets

1 sf1-e3.wired.net (206.221.193.1) 3.135 ms 3.021 ms 3.616 ms

2 sf0-e2s2.wired.net (205.227.206.33) 1.829 ms 3.886 ms 2.772 ms

3 paloalto-cr10.bbnplanet.net (131.119.26.105) 5.327 ms 4.597 ms 5.729 ms

4 paloalto-br1.bbnplanet.net (131.119.0.193) 4.842 ms 4.615 ms 3.425 ms

5 sl-sj-2.sprintlink.net (4.0.1.66) 7.488 ms 38.804 ms 7.708 ms

6 144.232.8.81 (144.232.8.81) 6.560 ms 6.631 ms 6.565 ms

7 144.232.4.97 (144.232.4.97) 7.638 ms 7.948 ms 8.129 ms

8 144.228.146.50 (144.228.146.50) 9.504 ms 12.684 ms 16.648 ms

9 f5-0.inr-666-eva.berkeley.edu (198.128.16.21) 9.762 ms 10.611 ms 10.403 ms

10 f0-0.inr-107-eva.Berkeley.EDU (128.32.2.1) 11.478 ms 10.868 ms 9.367 ms

11 f8-0.inr-100-eva.Berkeley.EDU (128.32.235.100) 10.738 ms 11.693 ms 12.520 ms

SQL Interview Question and Answer

2012-11-04T22:03:00.001-08:00

What are categories of SQL commands?

Data Definition Language (DDL)
Data Manipulation Language (DML)
Data Query Language (DQL)
Data Control Language (DCL)
Data Administration Commands (DAC)
Transactional Control Commands (TCC)

What Is Database is a collection of data. It contains information about one particular enterprise. A database management system (DBMS) consists of a collection of interrelated data and a set of programs to access that data.

What are the advantages of database?

Redundancy can be reduced
The data can be shared
Inconsistency can be avoided
Standards can be enforced
Security can be enforced
Integrity can be maintaned

DDL stands for Data Definition Language. Data Definition Language is used to create, alter and delete database objects.

DML

DML stands for Data Manipulation Language.
Data Manipulation Language commands let users insert, modify and delete the data in the database.
Sql provides three data manipulation statements insert, update and delete

What is SQL

SQL is structured Query Language which is a computer language for storing, manipulating and retrieving data stored in relational database.

SQL is the standard language for Relation Database System. All relational database management systems like MySQL, MS Access, Oracle, Sybase, Informix, postgres and SQL Server uses SQL as standard database language.

Also they are using different dialects, Such as:

 MS SQL Server using T-SQL,

 Oracle using PL/SQL,

 MS Access version of SQL is called JET SQL (native format )etc

Why SQL?

 Allow users to access data in relational database management systems.

 Allow users to describe the data.

 Allow users to define the data in database and manipulate that data.

 Allow to embed within other languages using SQL modules, libraries & pre-compilers.

 Allow users to create and drop databases and tables.

 Allow users to create view, stored procedure, functions in a database.

 Allow users to set permissions on tables, procedures, and views

Explain the difference between a hot backup and a cold backup.

A cold backup is done when there is no user activity going on with the system. Also called as offline backup, is taken when the database is not running and no users are logged in. all files of the database are copied and no changes during the copy are made.

A hot backup is taken when the database needs to run all the time. It is an online backup. All files of the database are copied and there may be changes to the database during the copy.

How many memory layers are in the oracle shared pool? Explain them

Oracles shared pool consists of two layers namely, Library cache and Data dictionary cache.

Library cache: This layer has information about SQL statements that were parsed, information about cursors and any plan data.

Data Dictionary cache: this Layer has information about the accounts of the users, their privileges and segments information.

What is the cache hit ratio, what impact does it have on performance of an Oracle database and what is involved in tuning it?

When the cache client like a CPU, web browser etc finds a successful entry in the cache memory, it is called as a cache hit. The percentage of these successful cache hits is called as cache hit ratio. Higher the cache hit ratio better will be the performance because data read from the cache is faster than the memory.

Explain the concept of the DUAL table.

On installing Oracle database, DUAL table Is present by default. It is a special table with just one row. It has a single column called DUMMY. The data type of this column in VARCHAR2(1). It has a value “X”. It is most commonly used to select pseudo columns in Oracle like sysdate.

Select sysdate from dual

SEO - Keyword Research

2012-11-03T00:24:00.002-07:00

In Keyword Research we choose the best keywords for our web pages.This is the most important part of SEO. We will choose the keywords which has good traffic volume. And we make sure that the keyword is related to our webpage.
For example:
Our website is related to water purifier service.
Water Purifier Service, water purifier center, water purifier repair, Ro reapir Service
So, we choose the related keywords for our web pages. In Keyword Research we will decide the targeted keywords for our webpage.

We use different tools for searching the keywords. Generally we prefer the free and best tools. In my opinion the free and best of all tools are:

.Google adwords keyword suggestion tool.
Word tracker keyword tool.
Manually

Pl/Sql - String Function

2012-11-02T22:36:00.003-07:00

1 ASCII(x);

Returns the ASCII value of the character x.

2 CHR(x);

Returns the character with the ASCII value of x.

3 CONCAT(x, y);

Concatenates the strings x and y and return the appended string.

4 INITCAP(x);

Converts the initial letter of each word in x to uppercase and returns that string.

5 INSTR(x, find_string [, start] [, occurrence]);

Searches for find_string in x and returns the position at which it occurs.

6 INSTRB(x);

Returns the location of a string within another string, but returns the value in bytes.

7 LENGTH(x);

Returns the number of characters in x.

8 LENGTHB(x);

Returns the length of a character string in bytes for single byte character set.

9 LOWER(x);

Converts the letters in x to lowercase and returns that string.

10 LPAD(x, width [, pad_string]) ;

Pads x with spaces to left, to bring the total length of the string up to width characters.

11 LTRIM(x [, trim_string]);

Trims characters from the left of x.

12 NANVL(x, value);

Returns value if x matches the NaN special value (not a number), otherwise x is returned.

13 NLS_INITCAP(x);

Same as the INITCAP function except that it can use a different sort method as specified by NLSSORT.

14 NLS_LOWER(x) ;

Same as the LOWER function except that it can use a different sort method as specified by NLSSORT.

15 NLS_UPPER(x);

Same as the UPPER function except that it can use a different sort method as specified by NLSSORT.

16 NLSSORT(x);

Changes the method of sorting the characters. Must be specified before any NLS function; otherwise, the default sort will be used.

17 NVL(x, value);

Returns value if x is null; otherwise, x is returned.

18 NVL2(x, value1, value2);

Returns value1 if x is not null; if x is null, value2 is returned.

19 REPLACE(x, search_string, replace_string);

Searches x for search_string and replaces it with replace_string.

20 RPAD(x, width [, pad_string]);

Pads x to the right.

21 RTRIM(x [, trim_string]);

Trims x from the right.

22 SOUNDEX(x) ;

Returns a string containing the phonetic representation of x.

23 SUBSTR(x, start [, length]);

Returns a substring of x that begins at the position specified by start. An optional length for the substring may be supplied.

24 SUBSTRB(x);

Same as SUBSTR except the parameters are expressed in bytes instead of characters for the single-byte character systems.

25 TRIM([trim_char FROM) x);

Trims characters from the left and right of x.

26 UPPER(x);

Converts the letters in x to uppercase and returns that string.

Pl/Sql - Cursor

2012-10-31T03:15:00.001-07:00

A cursor is a temporary work area created in the system memory when a SQL statement is executed.A cursor contains information on a select statement and the rows of data accessed by it. This temporary work area is used to store the data retrieved from the database, and manipulate this data. A cursor can hold more than one row, but can process only one row at a time.

Defining a Cursor

A cursor is defined in the declarative part of the PL/SQL block by naming it and associating it with a query
CURSOR <cursorname> IS
SELECT statement;

Example

CURSOR emp_cur IS
SELECT empno, ename, job, sal
FROM emp;

A Cursor can be manipulated using
– OPEN
– FETCH
– CLOSE

Cursor must be declared before it can be referenced using the OPEN, CLOSE or FETCH statements

The OPEN Statement
    Initializes or opens a cursor
    Cursor must be opened before any rows are returned by the query
OPEN <cursorname>
Example --
           OPEN emp_cur;

The FETCH Statement
    Can be executed repeatedly until all rows have been retrieved
FETCH <cursorname> INTO var1, …, varN;
OR
FETCH <cursorname> INTO record_variable;
    Example
FETCH emp_cur INTO mrec;

The CLOSE Statement
    Closes the cursor and makes the active set undefined
CLOSE <cursorname>;
    Example
CLOSE emp_cur;

Example -

DECLARE
2
3      v_id emp.empno%TYPE;
4
5      CURSOR v_cursor IS SELECT empno FROM emp ORDER BY empno;
6 BEGIN
7
8      OPEN v_cursor;
9      LOOP
10
11          FETCH v_cursor INTO v_id;
12
13          EXIT WHEN v_cursor%NOTFOUND;
14          DBMS_OUTPUT.PUT_LINE('v_id = ' || v_id );
15      END LOOP;
16      CLOSE v_cursor;
17 END;
18 /

SQL- UNIQUE CONSTRAINT WITH EXAMPLES

2012-08-30T00:03:00.000-07:00

UNIQUE constraint uniquely identifies each record in a database table.The UNIQUE and PRIMARY KEY constraints both provide a guarantee for uniqueness for a column or set of columns.A PRIMARY KEY constraint automatically has a UNIQUE constraint defined on it. you can have many UNIQUE constraints per table, but only one PRIMARY KEY constraint per table.

Example--

For example, the following SQL creates a new table called CUSTOMERS and adds five columns. Here AGE column is set to UNIQUE, so that you can not have two records with same age:

CREATE TABLE CUSTOMERS(
       ID   INT              NOT NULL,
       NAME VARCHAR (20)     NOT NULL,
       AGE  INT              NOT NULL UNIQUE,
       ADDRESS  CHAR (25) ,
       SALARY   DECIMAL (18, 2),       
       PRIMARY KEY (ID)
);

If CUSTOMERS table has already been created, then to add a UNIQUE constraint to AGE column, you would write a statement similar to the following:

ALTER TABLE CUSTOMERS
   MODIFY AGE INT NOT NULL UNIQUE;

You can also use following syntax, which supports naming the constraint and multiple columns as well:

ALTER TABLE CUSTOMERS
   ADD CONSTRAINT myUniqueConstraint UNIQUE(AGE, SALARY);

DROP a UNIQUE Constraint:................................................

To drop a UNIQUE constraint, use the following SQL:

ALTER TABLE CUSTOMERS
   DROP CONSTRAINT myUniqueConstraint;

If you are using MySQL then you can use following syntax:

  ALTER TABLE CUSTOMERS
     DROP INDEX myUniqueConstraint;

SQL - CHECK Constraint

2012-08-29T00:05:00.001-07:00

The CHECK Constraint enables a condition to check the value being 
entered into a record. If the condition evaluates to false, the record 
violates the constraint and isn.t entered into the table.

Example -1

  1-create table Employee(

  2    ID                 VARCHAR2(4 BYTE) ,

  3    First_Name         VARCHAR2(10 BYTE),

  4    Last_Name          VARCHAR2(10 BYTE),

  5    Start_Date         DATE,

  6    End_Date           DATE,

  7    Salary             Number(8,2),

  8    City               VARCHAR2(10 BYTE),

  9    Description        VARCHAR2(15 BYTE)

 10  )

 11  /

..............................................................................................................................................................

insert into Employee(ID,  First_Name, Last_Name, Start_Date,                     End_Date,                       Salary,  City,       Description)

  2               values ('01','Jason',    'Martin',  to_date('19960725','YYYYMMDD'), to_date('20060725','YYYYMMDD'), 1234.56, 'Toronto',  'Programmer')

  3  /



1 row created.



insert into Employee(ID,  First_Name, Last_Name, Start_Date,                     End_Date,                       Salary,  City,       Description)

  2                values('02','Alison',   'Mathews', to_date('19760321','YYYYMMDD'), to_date('19860221','YYYYMMDD'), 6661.78, 'Vancouver','Tester')

  3  /



1 row created.



insert into Employee(ID,  First_Name, Last_Name, Start_Date,                     End_Date,                       Salary,  City,       Description)

  2                values('03','James',    'Smith',   to_date('19781212','YYYYMMDD'), to_date('19900315','YYYYMMDD'), 6544.78, 'Vancouver','Tester')

  3  /



1 row created.



insert into Employee(ID,  First_Name, Last_Name, Start_Date,                     End_Date,                       Salary,  City,       Description)

  2                values('04','Celia',    'Rice',    to_date('19821024','YYYYMMDD'), to_date('19990421','YYYYMMDD'), 2344.78, 'Vancouver','Manager')

  3  /



1 row created.



insert into Employee(ID,  First_Name, Last_Name, Start_Date,                     End_Date,                       Salary,  City,       Description)

  2                values('05','Robert',   'Black',   to_date('19840115','YYYYMMDD'), to_date('19980808','YYYYMMDD'), 2334.78, 'Vancouver','Tester')

  3  /



1 row created.



insert into Employee(ID,  First_Name, Last_Name, Start_Date,                     End_Date,                       Salary, City,        Description)

  2                values('06','Linda',    'Green',   to_date('19870730','YYYYMMDD'), to_date('19960104','YYYYMMDD'), 4322.78,'New York',  'Tester')

  3  /



1 row created.



insert into Employee(ID,  First_Name, Last_Name, Start_Date,                     End_Date,                       Salary, City,        Description)

  2                values('07','David',    'Larry',   to_date('19901231','YYYYMMDD'), to_date('19980212','YYYYMMDD'), 7897.78,'New York',  'Manager')

  3  /



1 row created.



insert into Employee(ID,  First_Name, Last_Name, Start_Date,                     End_Date,                       Salary, City,        Description)

  2                values('08','James',    'Cat',     to_date('19960917','YYYYMMDD'), to_date('20020415','YYYYMMDD'), 1232.78,'Vancouver', 'Tester')

  3  /



1 row created.

select * from Employee
 




ID   FIRST_NAME           LAST_NAME            START_DAT END_DATE      SALARY CITY       DESCRIPTION

---- -------------------- -------------------- --------- --------- ---------- ---------- ---------------

01   Jason                Martin               25-JUL-96 25-JUL-06    1234.56 Toronto    Programmer

02   Alison               Mathews              21-MAR-76 21-FEB-86    6661.78 Vancouver  Tester

03   James                Smith                12-DEC-78 15-MAR-90    6544.78 Vancouver  Tester

04   Celia                Rice                 24-OCT-82 21-APR-99    2344.78 Vancouver  Manager

05   Robert               Black                15-JAN-84 08-AUG-98    2334.78 Vancouver  Tester

06   Linda                Green                30-JUL-87 04-JAN-96    4322.78 New York   Tester

07   David                Larry                31-DEC-90 12-FEB-98    7897.78 New York   Manager

08   James                Cat                  17-SEP-96 15-APR-02    1232.78 Vancouver  Tester



8 rows selected.

  1  ALTER TABLE employee

  2  ADD CONSTRAINT status_ck

  3  CHECK (city IN ('Vancouver', 'Toronto', 'New York'));



Table altered.

  1        insert into Employee(City)

  2                values('AAA')

  3  /

insert into Employee(City)

*

ERROR at line 1:

ORA-02290: check constraint (JAVA2S.STATUS_CK) violated

..................................................................................

Example: 2

For example, the following SQL creates a new table called CUSTOMERS and adds five columns. Here we add a CHECK with AGE column, so that you can not have any CUSTOMER below 18 years:

CREATE TABLE CUSTOMERS(
       ID   INT              NOT NULL,
       NAME VARCHAR (20)     NOT NULL,
       AGE  INT              NOT NULL CHECK (AGE >= 18),
       ADDRESS  CHAR (25) ,
       SALARY   DECIMAL (18, 2),       
       PRIMARY KEY (ID)
);

If CUSTOMERS table has already been created, then to add a CHECK constraint to AGE column, you would write a statement similar to the following:

ALTER TABLE CUSTOMERS
   MODIFY AGE INT NOT NULL CHECK (AGE >= 18 );

You can also use following syntax, which supports naming the constraint and multiple columns as well:

ALTER TABLE CUSTOMERS
   ADD CONSTRAINT myCheckConstraint CHECK(AGE >= 18);

DROP a CHECK Constraint:

To drop a CHECK constraint, use the following SQL. This syntax does not work with MySQL:

ALTER TABLE CUSTOMERS
   DROP CONSTRAINT myCheckConstraint;

SQL - Alias Syntax

2012-08-28T03:13:00.000-07:00

You can rename a table or a column temporarily by giving another name known as alias.
The use of table aliases means to rename a table in a particular SQL statement. The renaming is a temporary change and the actual table name does not change in the database.
The column aliases are used to rename a table's columns for the purpose of a particular SQL query.

The basic syntax of table alias is as follows:

SELECT column1, column2....
FROM table_name AS alias_name
WHERE [condition];

The basic syntax of column alias is as follows:

SELECT column_name AS alias_name
FROM table_name
WHERE [condition];

Example:

Consider following two tables, (a) CUSTOMERS table is as follows:

+----+----------+-----+-----------+----------+
| ID | NAME     | AGE | ADDRESS   | SALARY   |
+----+----------+-----+-----------+----------+
|  1 | Ramesh   |  32 | Ahmedabad |  2000.00 |
|  2 | Khilan   |  25 | Delhi     |  1500.00 |
|  3 | kaushik  |  23 | Kota      |  2000.00 |
|  4 | Chaitali |  25 | Mumbai    |  6500.00 |
|  5 | Hardik   |  27 | Bhopal    |  8500.00 |
|  6 | Komal    |  22 | MP        |  4500.00 |
|  7 | Muffy    |  24 | Indore    | 10000.00 |
+----+----------+-----+-----------+----------+

(b) Another table is ORDERS as follows:

+-----+---------------------+-------------+--------+
|OID  | DATE                | CUSTOMER_ID | AMOUNT |
+-----+---------------------+-------------+--------+
| 102 | 2009-10-08 00:00:00 |           3 |   3000 |
| 100 | 2009-10-08 00:00:00 |           3 |   1500 |
| 101 | 2009-11-20 00:00:00 |           2 |   1560 |
| 103 | 2008-05-20 00:00:00 |           4 |   2060 |
+-----+---------------------+-------------+--------+

Now following is the usage of table alias:

SELECT C.ID, C.NAME, C.AGE, O.AMOUNT 
        FROM CUSTOMERS AS C, ORDERS AS O
        WHERE  C.ID = O.CUSTOMER_ID;

This would produce following result:

+----+---------+-----+--------+
| ID | NAME    | AGE | AMOUNT |
+----+---------+-----+--------+
|  3 | kaushik |  23 |   3000 |
|  3 | kaushik |  23 |   1500 |
|  2 | Ramesh  |  25 |   1560 |
|  4 | kaushik |  25 |   2060 |
+----+---------+-----+--------+

Following is the usage of column alias:

 SELECT  ID AS CUSTOMER_ID, NAME AS CUSTOMER_NAME
     FROM CUSTOMERS
     WHERE SALARY IS NOT NULL;

This would produce following result:

+-------------+---------------+
| CUSTOMER_ID | CUSTOMER_NAME |
+-------------+---------------+
|           1 | Ramesh        |
|           2 | Ramesh        |
|           3 | kaushik       |
|           4 | kaushik       |
|           5 | Hardik        |
|           6 | Komal         |
|           7 | Muffy         |
+-------------+---------------+

Primary key vs. unique key

2012-08-23T04:31:00.004-07:00

One difference is that a unique key constraint can be created over columns with null values, while a primary key constraint does not allow null values. The other difference is that there can only be one primary key constraint defined on a table, but there can be multiple unique key constraints defined on a table.