Transact-SQL (T-SQL)

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Transact-SQL

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Transact-SQL (T-SQL) is Microsoft's and Sybase's proprietary extension toSQL. SQL, often expanded to Structured Query Language, is astandardized computer language that was originally developed by IBM for querying, altering and defining relational databases, usingdeclarative statements. T-SQL expands on the SQL standard to includeprocedural programming,local variables, various support functions for string processing, date processing, mathematics, etc. and changes to theDELETE and UPDATE statements. These additional features make Transact-SQL Turing complete.

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.

Contents

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• 1Flow control
• 2Changes to DELETE and UPDATE statements
• 3BULK INSERT
• 4TRY CATCH
• 5See also
• 6External links

[edit]Flow control

Keywords for flow control in Transact-SQL include BEGIN and END, BREAK, CONTINUE, GOTO, IF andELSE, 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.

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()) = 1BEGIN   PRINT 'It is the weekend.'   PRINT 'Get some rest on the weekend!'ENDELSEBEGIN   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 aWHILE loop is given below.

DECLARE @i INTSET @i = 0 WHILE @i < 5BEGIN   PRINT 'Hello world.'   SET @i = @i + 1END

[edit]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 users   FROM users as u  INNER JOIN user_flags as f    ON u.id=f.id WHERE f.name = 'Idle'

[edit]BULK INSERT

BULK INSERT 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 on Microsoft's MSDN page.

[edit]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 transactionBEGIN TRAN BEGIN TRY   -- execute each statement   INSERT INTO MYTABLE(NAME) VALUES ('ABC')   INSERT INTO MYTABLE(NAME) VALUES ('123')    -- commit the transaction   COMMIT TRANEND TRYBEGIN CATCH   -- rollback the transaction because of error   ROLLBACK TRANEND CATCH

[edit]See also

• Adaptive Server Enterprise (Sybase)
• PL/SQL (Oracle)
• PL/pgSQL (PostgreSQL)

[edit]External links

• Sybase Transact-SQL User's Guide
• Transact-SQL Reference for SQL Server 2000 (MSDN)
• Transact-SQL Reference for SQL Server 2005 (MSDN)
• Transact-SQL Reference for SQL Server 2008 (MSDN)