Transact-SQL

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.

Variables

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.'

and ENDmark a block of statements. If more than one statement is to be controlled by the conditional in the example above, we can use BEGINand ENDlike 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

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 WHILEloop, while 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 INSERT

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.

TRY CATCH

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

 

Text is available under the Creative Commons Attribution-ShareAlike License; additional terms may apply. By using this site, you agree to the Terms of Use and Privacy Policy.