The CALL statement invokes a procedure that has been previously created with a CREATE PROCEDURE statement. When the procedure
completes, any INOUT or OUT parameter value is copied back.
The argument list can be specified by position or by using keyword format. By position, the arguments match up with the corresponding
parameter in the parameter list for the procedure. By keyword, the arguments are matched up with the named parameters.
Procedure arguments can be assigned default values in the CREATE PROCEDURE statement, and missing parameters are assigned
the default value. If no default is set, and an argument is not provided, an error is given.
If the procedure being called returns an INT and the value is NULL, then the error status value, 0, is returned instead. There
is no way to differentiate between this case and the case of an actual value of 0 being returned.
Use of this statement to invoke a function is deprecated. If you have a function you want to call, consider using an assignment
statement to invoke the function and assign its result to a variable. For example:
Core feature. The use of the RETURN statement to return a value from a stored procedure is a vendor extension; SQL/2008
supports return values only for SQL-invoked functions, not for procedures. Default values for stored procedure arguments are
not supported in SQL/2008.
Call the ShowCustomers procedure. This procedure has no parameters, and returns a result set.
The following Interactive SQL example creates a procedure to return the number of orders placed by the customer whose ID is
supplied, creates a variable to hold the result, calls the procedure, and displays the result.
CREATE PROCEDURE OrderCount (IN customer_ID INT, OUT Orders INT)
KEY LEFT OUTER JOIN SalesOrders
WHERE Customers.ID = customer_ID;
-- Create a variable to hold the result
CREATE VARIABLE Orders INT
-- Call the procedure, FOR customer 101
CALL OrderCount ( 101, Orders )
-- Display the result
SELECT Orders FROM DUMMY