T-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.

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

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.)

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:

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.

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

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