Transact-SQL

Transact-SQL (T-SQL) is Microsoft’s and Sybase’s proprietary extension to the SQL (Structured Query Language) used to interact with relational databases. T-SQL expands on the SQL standard to include procedural programming, local variables, various support functions for string processing, date processing, mathematics, etc. and changes to the DELETE and UPDATE statements.

Transact-SQL is central to using Microsoft SQL Server. All applications that communicate with an instance of SQL Server do so by sending Transact-SQL statements to the server, regardless of the user interface of the application

Variables

Transact-SQL provides the following statements to declare and set local variables: DECLARE, SET and SELECT.

DECLARE @var1 NVARCHAR(30)

SET @var1 = ‘Some Name’

SELECT @var1 = Name

FROM Sales.Store

WHERE CustomerID = 100

Flow control

Keywords for flow control in Transact-SQL include BEGIN and END, BREAK, CONTINUE, GOTO, IF and ELSE, RETURN, WAITFOR, and WHILE.

IF and ELSE allow conditional execution. This batch statement will print “It is the weekend” if the current date is a weekend day, or “It is a weekday” if the current date is a weekday. (Note: This code assumes that Sunday is configured as the first day of the week in the @@DATEFIRST setting.)

IF DATEPART(dw, GETDATE()) = 7 OR DATEPART(dw, GETDATE()) = 1

PRINT ‘It is the weekend.’

ELSE

PRINT ‘It is a weekday.’

BEGIN and END mark a block of statements. If more than one statement is to be controlled by the conditional in the example above, we can use BEGIN and END like this:

IF DATEPART(dw, GETDATE()) = 7 OR DATEPART(dw, GETDATE()) = 1

BEGIN

PRINT ‘It is the weekend.’

PRINT ‘Get some rest on the weekend!’

END

ELSE

BEGIN

PRINT ‘It is a weekday.’

PRINT ‘Get to work on a weekday!’

END

WAITFOR will wait for a given amount of time, or until a particular time of day. The statement can be used for delays or to block execution until the set time.

RETURN is used to immediately return from a stored procedure or function.

BREAK ends the enclosing WHILE loop, while CONTINUE causes the next iteration of the loop to execute. An example of a WHILE loop is given below.

DECLARE @i INT

SET @i = 0

 

WHILE @i < 5

BEGIN

PRINT ‘Hello world.’

SET @i = @i + 1

END

Changes to DELETE and UPDATE statements

In Transact-SQL, both the DELETE and UPDATE statements allow a FROM clause to be added, which allows joins to be included.

This example deletes all users who have been flagged with the ‘Idle’ flag.

DELETE u

FROM users AS u

INNER JOIN user_flags AS f

ON u.id = f.id

WHERE f.name = ‘idle’

BULK INSERT

BULK is a Transact-SQL statement that implements a bulk data-loading process, inserting multiple rows into a table, reading data from an external sequential file. Use of BULK INSERT results in better performance than processes that issue individual INSERT statements for each row to be added. Additional details are available in MSDN.

TRY CATCH

Beginning with SQL Server 2005, Microsoft introduced additional TRY CATCH logic to support exception type behaviour. This behaviour enables developers to simplify their code and leave out @@ERROR checking after each SQL execution statement.

— begin transaction

BEGIN TRAN

 

BEGIN TRY

— execute each statement

INSERT INTO MYTABLE(NAME) VALUES (‘ABC’)

INSERT INTO MYTABLE(NAME) VALUES (‘123’)

 

— commit the transaction

COMMIT TRAN

END TRY

BEGIN CATCH

— roll back the transaction because of error

ROLLBACK TRAN

END CATCH

 

Source: Wikipedia

For more details or to start new programming projects please Contact Us

CONTACT US

We're not around right now. But you can send us an email and we'll get back to you, asap.

Sending

©2018 Powered by Networx Security e.V.

Log in with your credentials

Forgot your details?