Imposes conditions on the execution of a Transact-SQL statement. The Transact-SQL statement that follows an IF keyword and its condition is executed if the condition is satisfied: the Boolean expression returns TRUE. The optional ELSE keyword introduces another Transact-SQL statement that is executed when the IF condition is not satisfied: the Boolean expression returns FALSE.
An IF...ELSE construct can be used in batches, in stored procedures, and in ad hoc queries. When this construct is used in a stored procedure, it is frequently used to test for the existence of some parameter.
IF tests can be nested after another IF or following an ELSE. The limit to the number of nested levels depends on available memory.
The following example uses IF…ELSE with output from the uspGetList stored procedure. This stored procedure is defined in Creating Stored Procedures. In this example, the stored procedure returns a list of bikes with a list price less than $700. This causes the first PRINT statement to execute.
DECLARE @compareprice money, @cost money EXECUTE Production.uspGetList '%Bikes%', 700, @compareprice OUT, @cost OUTPUT IF @cost <= @compareprice BEGIN PRINT 'These products can be purchased for less than $'+RTRIM(CAST(@compareprice AS varchar(20)))+'.' END ELSE PRINT 'The prices for all products in this category exceed $'+ RTRIM(CAST(@compareprice AS varchar(20)))+'.'
For more examples, see ELSE (IF...ELSE) (Transact-SQL).