Sometime a stored procedure not only want to take input values from the calling statement batch, but it also want to send output values back to the calling statement batch. This can be done by defining output parameters in the CREATE PROCEDURE statement.

To define an output parameter, you should use this format: "@parameter_name data_type OUTPUT", as shown in the following tutorial exercise:

DROP PROCEDURE diff_in_days;

GO

-- Defining an output parameter

CREATE PROCEDURE diff_in_days

@start_date DATETIME,

@end_date DATETIME = '19-May-2007',

@days VARCHAR(40) OUTPUT

AS BEGIN

SET @days = CONVERT(VARCHAR(20),@end_date,107)

+ ' - '

+ CONVERT(VARCHAR(20),@start_date,107)

+ ' = '

+ STR(DATEDIFF(DAY, @start_date, @end_date));

END;

GO

Command(s) completed successfully.

EXEC diff_in_days

@start_date='01-Jan-2007'

GO

Msg 201, Level 16, State 4, Procedure diff_in_days, Line 0

Procedure or Function 'diff_in_days' expects

parameter '@days', which was not supplied.