Boolean_expression

Is an expression that returns TRUE or FALSE. If the Boolean expression contains a SELECT statement, the SELECT statement must be enclosed in parentheses.

{ sql_statement | statement_block }

Is any Transact-SQL statement or statement grouping as defined by using a statement block. Unless a statement block is used, the IF or ELSE condition can affect the performance of only one Transact-SQL statement.

To define a statement block, use the control-of-flow keywords BEGIN and END.

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)))+'.'

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