Variables in T-SQL

Variables can be used to store the data in temporally based on data type.

Variable name begin with @ symbol.

There are two types of variables in T-SQL.

1. Local Variables (It must begin @ symbol).

2. Global Variables (it must begin @@ symbol) this variables also known as system variables.

Syntax Declare a Variable

DECLARE @Variable-Name DATATYPE

EXAMPLE:

DECLARE @Name VARCHAR(100)

In before 2008 versions of SQL SERVER we declare a variable and assign a value in 2 lines.

DECLARE @Name VARCHAR(100)

SET @Name='LeadFirstSQL'

In 2008 and Later versions of SQL SERVER we declare a variable and assign a value in single line.

DECLARE @Name VARCHAR(100) ='LeadFirstSQL'

Variables must be declare and used with the same batch.

DECLARE @Name VARCHAR(100) ='LeadFirstSQL'

SELECT @Name AS Nam

SELECT @Name AS Name

If we are trying to execute above statement we get the error. Because of before the GO all the Queries are treated as single batch after the GO it treated as different batch.

Msg 137, Level 15, State 2, Line 1

Must declare the scalar variable "@Name".

We can also use variables as Table Valued Parameters.

Comments

Coalesce function

Coalesce function returns the first non-null value among the arguments. Syntax: Coalesce (expression [,..n]) Here is example using Coalesce function Example 1 DECLARE @Str1 varchar ( 10 ), @str2 varchar ( 20 ), @Str3 varchar ( 20 ) SET @Str2 = 'Sql' , @Str3 = 'Server' SELECT COALESCE ( @Str1 , @str2 , @Str3 ) As [Coalesce] In above example @Str2 value is ‘Sql’ , @str3 value is ‘Server’ and @str1 values is Null because it not assigned any value . Output: It return’s “Sql” because Coalesce function return’s first non null value. Example 2: Coalesce in select statement. IF OBJECT_ID ( 'Employee' , 'U' ) IS NOT NULL DROP TABLE Employee CREATE TABLE Employee ( ID INT IDENTITY ( 1 , 1 ) PRIMARY KEY , NAME VARCHAR ( 20 ), SALARY INT ) INSERT INTO Employee ( NAME , SALARY ) VALUES ( 'Rakesh' , 5000 ),(NULL, 6000 ),( 'Naresh...

IDENTITY COLUMNS

Identity column specifies when ever new value is inserted into table. Identity column automatically inserted value into column. Identity Column can be specified at the time of creation of table. CREATE TABLE Employee ( EMPID INT IDENTITY ( 1 , 1 ), EMPNAME VARCHAR ( 50 ), SALARY INT ) In above table creation script EMPID column specifies IDENTITY property i.e., whenever a new row inserted into a Employee table EMPID Column will automatically value is inserted. INSERT INTO Employee ( EMPNAME , SALARY ) VALUES ( 'RAKESH' , 7000 ) INSERT INTO Employee ( EMPNAME , SALARY ) VALUES ( 'ALI' , 12000 ) SELECT * FROM Employee When u run above select statement is the following result is if u are trying insert value into identify columns .it will give error. INSERT INTO Employee ( EMPID , EMPNAME , SALARY ) VALUES ( 1 , 'RAKESH' , 7000 ) Msg 5...

CONCAT FUNCTION IN SQL SERVER 2012

Concat function is used concatnating the values among the different arguments. Syntax: Concat([String1],[String2]..[StringN]); DECLARE @FName VARCHAR ( 50 ), @LName VARCHAR ( 50 ); SET @FName = 'Rakesh' ; SET @LName = 'Kalluri' ; SELECT CONCAT ( @FName , ' ' , @LName ) as [FullName] ; Output: Rakesh Kalluri --Before SQL 2012 Versions we can use like this way DECLARE @FName VARCHAR ( 50 ), @LName VARCHAR ( 50 ); SET @FName = 'Rakesh' ; SET @LName = 'Kalluri' ; SELECT @FName + ' ' + @LName as [FullName] ; Output: Rakesh Kalluri --But Before SQL 2012 Versions there are 2 problems when we contacting . --1.Need to replace NULL Value to Empty.if we directly concat NULL Value the Entire result also NULL. --Before 2012: DECLARE @FName VARCHAR ( 50 ), @LName VARCHAR ( 50 ); SET @FName = 'Rakesh' ; SELECT @FName + ' ' + @LName a...

Tech Learn

Search This Blog