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.
Transact-SQL provides the following statements to declare and set local variables:
DECLARE @var1 NVARCHAR(30) SET @var1 = 'Some Name' SELECT @var1 = Name FROM Sales.Store WHERE CustomerID = 100
Keywords for flow control in Transact-SQL include
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
IF DATEPART(dw, GETDATE) = 7 OR DATEPART(dw, GETDATE) = 1 PRINT 'It is the weekend.' ELSE PRINT 'It is a weekday.'
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
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
In Transact-SQL, both the
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 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.
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
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