SQL For Beginners

How to handle erros in T-SQL code ?

2014-05-25T00:29:00.001-07:00

From SQL Server 2005 introduced a TRY ... CATCH statements that you can use to provide error handling.

A TRAY block must be followed immediately by a single CATCH block
When an error occurs in a statement within a TRY block, control is passed to the CATCH block where the error can be processed. If no error occurs inside the TRY block, the CATCH block is skipped.
Within a CATCH block, you can use the functions shown in this figure to return data about the error that caused the CATCH block to be executed.

Syntax:

BEGIN TRY
{sql_statement / statement block}
END TRY
BEGIN CATCH
{sql_statement / statement block}
END CATCH

How to test the existence of a database object ?

2014-05-25T00:01:00.000-07:00

OBJECT_ID is used to check the existence of the table and DB_ID is used to check the existence of the Database.

Syntax of the OBJECT_ID function

<pre class="brush:sql;">

OBJECT_ID(‘object/table’)

</pre>

Syntax of the DB_ID function

<pre class="brush:sql;">

DB_ID(‘database’)

</pre>

EXAMPLES:

Code that tests whether a database exists before it deletes it

<pre class="brush:sql;">

IF DB_ID(‘Test_DB’) IS NOT NULL

DROP DATABASE Test_DB

CREATE DATABASE Test_DB

</pre>

Code that tests for the existence of the talbe

<pre class="brush:sql;">

IF OBJECT_ID(‘Test_Table’) IS NOT NULL

DROP TABLE Test_Table

</pre>

Another way to test the existence of a table

<pre class="brush:sql;">

IF EXISTS ( SELECT * FROM sys.tables where name = ‘Test_Table’)

DROP TABLE Test_Table

</pre>

Code that tests for the existence of the temp table

<pre class="brush:sql;">

IF OBJECT_ID(‘tempdb..#temptable_name’) IS NOT NULL

DROP TABLE #temptable_name

</pre>

Types of Transact-SQL Table Objects

2014-05-24T23:35:00.000-07:00

There are Five Types of Transact-SQL Table Objects

#	Type	Scope
1	Standard Table	Available within the system until explicitly deleted
2	Temporary Table	Available within the system while the current database session is open
3	Table Variable	Available within a script while the current batch is executing
4	Derived Table	Available within a statement while the current statement is executing
5	View	Available within the system until explicitly deleted

Note:

Derived Tables are select Statements in from clause, referred by an alias name.
CTE (Common table expression) is a type of derived table.

Diffence between Table Variable and Temp Table

2014-05-04T11:53:00.000-07:00

#.	Table Variable	Temp Table
1	It stored in primary memory(ie. in RAM)	It stored in system database(ie. In msdb)
2	It has batch scope only, ie. Till the current t-sql stmt to be execute	It has the scope till the query window close, In case of local temp table and has the scope till all the SSMS query windows close in case of global temp table
3	Table variables can’t use within select into clause	Temp tables can be used within select into clause
4	Table variables gives better performance than temp table, because they stores in primary memory (ie. In RAM)	Temp tables not gives better performance than table variables, because it stores in hard disk
5	We can’t explicitly drop the table variables	We can explicitly drop the temp tables

Difference between UNION and UNION ALL ?

2014-05-04T11:18:00.000-07:00

UNION and UNION ALL both are used to combine the results sets into one single results set, But following are the difference between the both operators.

#.	UNION	UNION ALL
1	UNION removes duplicate records from the two or more results sets	UNION ALL doen’t remove duplicate records from the two or more results sets
2	UNION Sorts the data from the results sets	UNION ALL doesn’t Sorts the data from the results sets
3	By compare with union all, union is much less performance. Because of it must scan the result for duplicates	UNION ALL performance is more comparing with UNION

SET Operators in T-SQL

2014-05-04T10:32:00.000-07:00

Set Operators :

It is used to combine multiple results sets into one single result set.

There are 3 set operators in T-SQL
1) UNION/UNION ALL
2) EXCEPT
3) INTERSECT

UNION/UNION ALL :
----------------------------
It is used to combine two or more result sets into one single result set by with or without duplicates
(ie, UNION doesn't allow null values, but UNION ALL allows null values)

Example:
<<ResultSet>>
UNION or UNION ALL
<<ResultSet>>

EXCEPT:
------------
It takes the data from one result set where there is no matching in another result set.

Example:
<<ResultSet>>
EXCEPT
<<ResultSet>>

INTERSECT:
----------------
It takes the data from the result sets which are in common

Example:
<<ResultSet>>
INTERSECT
<<ResultSet>>

How to change the Identity Column value ?

2014-05-04T09:19:00.000-07:00

Before Change the Identity value(ProductID column) from the Product Table

-- To set the new identity value on the Product Table

DBCC CHECKIDENT ('Product', RESEED, 10)

Execution Results as follows

Checking identity information: current identity value '10', current column value '10'.
DBCC execution completed.

To insert a new record in the product table, to test the next identity value

insert into Product values ('Mat',200)

After Change the Identity value

How to check the current identiy value in a table ?

2014-05-04T09:00:00.000-07:00

"DBCC CHECKIDENT" Statement is used to check the current identity value for the specified table and if requires then can modify/change the identity value on a identity column.

Syntax:
DBCC CHECKIDENT ('Table_Name' [ , { NORESEED | { RESEED [ , new_reseed_value ] } } ] )

Example:

CREATE TABLE Product(ProductID int identity(1,1), ProductName varchar(20), Price decimal(18,6) )

INSERT INTO Product VALUES ('Book',150.10),('Pen',35.50)

-- To check the current maximum identity value in the column, execute the following statement


DBCC CHECKIDENT ('Product', NORESEED)

Database States

2014-04-29T12:11:00.003-07:00

MS SQL Server Database will be in any of the states.

ONLINE: Database is available for access.
OFFLINE: Database is unavailable.
RESTORING: Database Restore is not completed, so The database is unavailable.
RECOVERING: Database is being recovered. the database state will become online if the recovery succeeds.
RECOVERY PENDING: recovery is failed due to missing resources, Additional action by the user is required to resolve the error and let the recovery process be completed.
SUSPECT: database may be damaged. Additional is required to resolve the problem.
EMERGENCY: This state prevent all the changes, It allows only readonly and access is limited to members of the sysadmin fixed server role. EMERGENCY is primarily used for troubleshooting purposes.

To verify the current state of a database, following SQL Queries or system funtions will be useful:

SELECT name,state_desc FROM sys.databases

SELECT DATABASEPROPERTYEX ( 'Test' , 'status' )

System Databases

2014-04-29T11:48:00.001-07:00

SQL Server includes the following system databases:

master - captures all the information about an SQL instance
msdb - used by SQL Server agent(schedule alerts & jobs)
model - Database Template for creating new DB
Resource - read only database, contains system objects which are logically accessed via all the db via sys schema
tempdb - storage for temporary objects

Microsoft SQL Server Code Names

2014-04-29T11:08:00.001-07:00

Microsoft has given codenames to all their products, Here is the list of the code name of which are assigned to each version of SQL Server Products.

In 1988, Microsoft released its first version of SQL Server. It was developed jointly by Microsoft and Sybase for the OS/2 platform.

1993 – SQL Server 4.21 for Windows NT
1995 – SQL Server 6.0, codenamed SQL95
1996 – SQL Server 6.5, codenamed Hydra
1999 – SQL Server 7.0, codenamed Sphinx
1999 – SQL Server 7.0 OLAP, codenamed Plato
2000 – SQL Server 2000 32-bit, codenamed Shiloh (version 8.0)
2003 – SQL Server 2000 64-bit, codenamed Liberty
2005 – SQL Server 2005, codenamed Yukon (version 9.0)
2008 – SQL Server 2008, codenamed Katmai (version 10.0)
2010 – SQL Server 2008 R2, Codenamed Kilimanjaro (aka KJ)
2012– SQL Server 2012, Codenamed Denali (version 11.0)
2012 - SQL Server Data Tools, Codenamed Juneau (Next CTP Of Denali)
2012 - SQL Server Data Tools, Codenamed Crescent(Included in Denali Version)
2014 - SQL Server In-Memory OLTP, Codenames Hekaton

Microsoft SQL Server 2012 Technologies

2014-04-29T10:48:00.002-07:00

Microsoft SQL Server is built with collection of tools/utilities for maintain/manage the data and Data analysis. Some of the tools are listed here:

Database Engine - RDBMS System
Data Quality Services(DQS) - Perform data cleansing by using cloud-based reference data services
Analysis Services - Provides OLAP & Data Mining Functionality
Integration Services - Perform data integration and data transformations solutions
Master Data Services - Solution for MDM
Replication - Data distribution/Copy Technology from one DB to another
Reporting Services - Rich reporting tool

We will look at it in details in next posts.

SQL Server 2008 New Features

2014-04-25T11:30:00.000-07:00

Microsoft SQL Server 2008 introduces several important new Transact SQL programmability features and enhances some existing ones

Following is the list of key new features

1.Initializing variables

2.Compound assignment operators

3.Enhanced CONVERT function

4.New date and time data types

5.New date and time functions

6.The MERGE statement

7.Grouping sets

8.Table valued parameters

9.Large user-defined types

10.Table value constructor support

11.DDL trigger enhancements

12.Sparse columns

13.Filtered indexes

We will provide the information in detail in next section.

How to import data directly from T-SQL commands without using SQL Server Integration Services?

2014-04-24T11:30:00.003-07:00

There are so many ways to import data directly using T-SQL.

Here listed couple of commands which helps to load the Data quickly into the Database:

BCP
Bulk Insert
OpenRowSet
OPENDATASOURCE
OPENQUERY

How to insert the values manually for the Identity Column ?

2014-04-23T10:22:00.000-07:00

What is Identity Column :

For Identity Column, SQL Server will provide the values automatically at the time of inserting each record in the table.

Example :

-- Creating the table

CREATE TABLE TestTable ( TestID INT NOT NULL IDENTITY(1,1) PRIMARY KEY, TestValue NVARCHAR(50) NOT NULL )

-- To insert value to the identity column

INSERT TestTable(TestId, TestValue) VALUES (1, 'record 1')

-- Cannot insert explicit value for identity column in table 'TestTable' when IDENTITY_INSERT is set to OFF.

SET IDENTITY_INSERT TestTable ON       -- Disable the Identity to Insert the values manually

INSERT TestTable(TestId, TestValue) VALUES (1, 'record 1')       -- Insert the values for the identity column

select * from TestTable

SET IDENTITY_INSERT TestTable OFF    -- Enable the Identity to Insert the values by the Server automatically

Differences between Stored procedures and User defined functions

2014-04-23T10:02:00.000-07:00

Difference 1:

Stored procedure used for perform specific tasks
Normally functions will be used for computing value

Difference 2:

Stored procedures may or may not return values
But function should return value

Difference 3:

Stored procedure cannot be used in the select/where/having clause
But function can be called from select/where/having clause

Difference 4:

Stored procedure can run independently. It can be executed using EXECUTE or EXEC command

But function cannot run independently, It has to be the part of the SQL statement

Difference 5:

Temporary table (derived) cannot be created on function
But it can be created in stored procedures

Difference 6:

From sql server 2005 onwards, TRY CATCH statements can be used in the stored procedures

But it cannot be used in the function. But we can use raise error function

Difference 7:

Stored procedure can call the user defined functions
But the function cannot call the stored procedures

The function cannot call the stored procedures like procedures. There are many types of stored procedures in sql server.

System Stored procedure
User defined Stored procedure
NET CLR stored procedure
Extended stored procedure

Except extended stored procedures no one can call the user defined functions

Difference 8:

Stored procedures can have input and output parameters
But the function can have only input parameters

Difference 9:

Stored procedures can have select and all DML operations
But the function can do only select operation

Functions will not allow to do the DML on existing tables. But still we can do the DML operation only on the table variable inside the user defined functions

Difference 10:

Function cannot have the transaction statements.

The transaction statement cannot be used in the function. Normally we won't do any DML operations in the function.

Stored procedure can use transaction statements

DISTINCT

2012-10-15T11:24:00.004-07:00

Distinct statement eliminates the duplicate data in the specified column from the table.

In a table, some of the columns may contain duplicate values. Sometimes you will want to list only the different (distinct) values in a table.

The DISTINCT keyword can be used to return only distinct (different) values.

DISTINCT Syntax:-

SELECT DISTINCT <Column_Name> FROM <Table_Name>

DISTINCT Example:-

We have a table called “salestaxRate” and columns are SalesTaxRateID, TaxType, TaxRate, Name, ModifiedDate as shown below...

Now we want to select only the distinct values (Different Values) from the column named "TaxRate" from the table above.

We use the following SELECT statement:

SELECT DISTINCT TaxRate FROM salestaxRate

The result-set will look like this

String Functions in SQL

2012-10-06T01:43:00.000-07:00

String Functions:-
Before we start look at the "String Functions", first we should understand what is string? and what is functions.

What is String?

In SQL, Collection of character or combination of word is called as "String". Data whichever stored using following datatype is called as string

Varchar

NVarchar

Text

Char

NChar

What is Functions?

Function is a set of code or procedure which will perform some specfic operation is known as functions.

What is String Functions?
The Function which is written to perform string related opearations like...

Findling character length

Searching some character from collection of texts/paragraphs

Replacing some character with new character

Spliting a word based on some delimiter

etc.,

Hope above explanation is helpful to understand about what is string functions

The following commands are the functions which are used to perform the string operations..

ASCII

NCHAR

SOUNDEX

CHAR

PATINDEX

SPACE

CHARINDEX

QUOTENAME

DIFFERENCE

REPLACE

STUFF

LEFT

REPLICATE

SUBSTRING

REVERSE

UNICODE

LOWER

RIGHT

UPPER

LTRIM

RTRIM

Note: We will Explain about each functions in detail in further posts..

Methods to Create a Table in DB

2012-09-23T03:50:00.001-07:00

In Previous post “SQL Table”, we’ve explained about the definition of the Table. This article will explain about “what are the ways we can create table in SQL Server”.

We can create a Table in Database in many ways, but most main method are,

Using SQL Scripts
Using Database Tool

Using SQL Scripts:

There are many database tools allow you to create tables without writing SQL State scripts, but given that tables are the container of all the data, all it is one of the fundamental object of the database, so it would be good if you learn thru SQL Scripts.

The CREATE TABLE statement is used to create a table in a database.

Syntax of CREATE TABLE:

Following are the basic syntax of creating a table

        Create table
        (
            column1 ,
            column2 ,
            column3 ,
            <...> <...> <...>
        )

Sample Table: EMPLOYEE

Execute the following Query at SQL Server management studio; it will create a Table called “Employee”

        Create table Employee
        (
            Emp_ID int not null,
            First_Name varchar(50),
            Last_Name varchar(50),
            Date_of_Joining date,
            Department varchar(50)
        )

Using Database Tool (SSMS):

In this method, we could create a table using the tool, SQL Server Management Studio(SSMS).

Follow the steps below to create a table.

1. Open SSMS from Start Menu as shown below

2. Login/connect to the SQL Server by providing proper credentials

3. After logged in, Decide the database in which you are planning to create a table. Here am planning to create a table under “TestDB”, refer the exhibit below

4. Right click on the the Node “Tables”, select “New Table”

5. A spreadsheet will appear with 3 columns like “Column Name”, “Data Type”, “Allow Nulls”

6. Fill the sheet with columns name and its data type as shown below

7. Click Save Button from the Toolbar or Press Ctrl+S Keys

8. You will see a popup window with a input field, enter the table name here , press OK Button

Now you can see a new Table, Which you created, under Tables Node.

Hope this helps!.. please leave your comments here if you need any help on this..

Happy Learning.. :)

SQL Table

2012-09-09T18:51:00.002-07:00

Tables are the basic structure where data is stored in the database. Hence table is one of the Database object.

Table consists of following Objects:-

Rows
Columns
Attributes
Relations
Data types
Constraints
etc.,

Table is a set of data elements (values) that is organized using a model of vertical columns and horizontal rows.

Note: A table has a specified number of columns but can have any number of rows.

What is RDBMS?

2012-09-09T11:30:00.000-07:00

RDBMS is stands for Relational DBMS.

RDBMS is the extension of DBMS.
DBMS is built to support relational Model is known as RDBMS
DBMS are for smaller organizations with small amount of data, where security of the data is not of major concern and RDBMS are designed to take care of large amounts of data and also the security of this data.
In the Relational Data Model, Data represents in the form of table.
DBMS that stores the data in the form of Related Tables is known as RDBMS.

Refer the screenshot to know about various components of the basic Relational Model “Table”

Advantages of RDBMS:-

Single database can be categorized/split across different tables, which is differ from flat-file database that has one single table to store the entire database data.
In RDBMS, Same Database can be analyzed/viewed in different ways
RDBMS Data is structured in form of DB tables, records, fields, etc.,

Example for RDBMS:-
The most popular RDBMS are MS SQL Server, DB2, Oracle, MySQL and MS Access

What is DBMS?

2012-08-28T12:13:00.001-07:00

DBMS stands for ... Database Management System.

This system is assisting us to manage/store the Data accurately and very easiest way

DBMS is a collection of programs which helps to handle the data in following ways..

    * Adding Data
    * Deleting Unnecessery Data
    * Modifying the Existing Record

A DBMS support various functions like data security, data integrity, data sharing, data concurrence, data independence, data recovery etc. However, all database management systems that are now available in the market like Sybase, Oracle, and MS-Access do not provide the same set of functions, though all are meant for data management.

How to Create Database?

2012-08-21T11:27:00.001-07:00

Database can be created using following ways:-

Using SQL Script
Using Wizard

SQL Script:-

Create Database statement is used to create a database in SQL Server.

Syntax:

Following SQL Syntax helps to create a database

CREATE DATABASE <database_Name>

Sample:

Execute the following Query at SQL Server management studio, it will create a Database named as “TestDB”

CREATE DATABASE TestDB

Wizard:-

Database can be created using SQL Server management studio, follow the steps given below to create a DB

1. Open SQL Server management studio from Program menu (start Menu)

2. Login/connect to the SQL Server by providing proper credentials

3. After connected to the server, Select the Database Node in the Object Explorer --> Right Click on the Database node, Select “New Database” (refer the Exhibit given below for further reference)

4. New Database Wizard will appear as shown below,
5. Enter the name of the database in “Database name” text field.

6. Click Ok to create the database

7. Once it is created, it will be display under database node as shown below

To Know More about Database, Refer the Article posted at,

http://blog-sqllearning.blogspot.in/2012/08/what-is-database.html

What is Database?

2012-08-18T06:01:00.001-07:00

Database is a system in which we can store and manage the data in the organized way. It is abbreviated as DB.

It is a Repository in which we can store the collections of data. data are stored in database in the form of tables and other database objects as mentioned below:-

Table - Combination of rows and columns
Tables - Collections of Table
Views - Virtual Table
Stored procedure & function - collection of logical scripts
etc.,

Relational Database Management System (RDBMS) helps to access the data information from the database.

Following are the examples of the RDBMS:-

MsAccess
SQL Server
Oracle
etc.,

Refer the article given below to know about "How to Create a Database"
http://blog-sqllearning.blogspot.in/2012/08/how-to-create-database.html

What is DCL?

2012-08-18T04:24:00.001-07:00

DCL stands for.. Data Control Language

DCL Provides the access permission over the data which is stored in the database.

DCL Commands Includes,

Grant - Command will permission to the user to do specific operations.
Revoke - command will remove the given permission from the user.

As mentioned above, DCL commands will allow or deny the following operations..
CONNECT
SELECT
INSERT
UPDATE
DELETE
EXECUTE