Transact-SQL (T-SQL) is Microsoft's and Sybase's proprietary extension to SQL. SQL, the acronym for Structured Query Language, is a standardized computer language that was originally developed by IBM for querying, altering and defining relational databases, using declarative statements. 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. 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.
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.'
ENDmark a block of statements. If more than one statement is to be controlled by the conditional in the example above, we can use
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
WAITFORWAITFOR 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.
RETURNRETURN is used to immediately return from a stored procedure or function.
BREAKBREAK ends the enclosing
CONTINUEcauses the next iteration of the loop to execute. An example of a
WHILEloop 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 INSERTis 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 INSERTresults in better performance than processes that issue individual
INSERTstatements for each row to be added. Additional details are available in MSDN.
Beginning with SQL Server 2005, Microsoft introduced additional
TRY CATCHlogic to support exception type behaviour. This behaviour enables developers to simplify their code and leave out
@@ERRORchecking 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 -- rollback the transaction because of error ROLLBACK TRAN END CATCH