Mysql – How does MySQL return a result set from a stored procedure

MySQLstored-procedures

I'm trying to get my head around stored procedures for use in a web application. It seems to me that whatever the last statement is in a MySQL stored procedure is seems to be what gets treated as that procedure's result set. Unfortunately though, it seems there are references in the MySQL docs that say a procedure can return multiple result sets. How is this behavior triggered? How can I tell the MySQL server that I explicitly want only one result set returned?

(For instance, I have a query that does a SELECT and a few inserts. I don't want to tell clients about the inserts, but I do want the client to be given the SELECT's result set….)

Best Answer

Each SELECT statement that does not insert into a table or a variable will produce a result set.

If you want your stored procedure to return only one result set, make sure that you only have one SELECT statement. If you have other SELECT statements, make sure that they insert results into a table or variable.

UPDATE
Here are examples of stored procedures.

This stored procedure would return one result set:

DELIMITER ;;
CREATE DEFINER=CURRENT_USER PROCEDURE stored_procedure_name()
BEGIN
    DECLARE local_variable_name INT;

    SELECT column_name FROM table_1 LIMIT 1 INTO local_variable_name;

    SELECT * FROM table_1;
END;;
DELIMITER ;

This stored procedure would return two result sets:

DELIMITER ;;
CREATE DEFINER=CURRENT_USER PROCEDURE stored_procedure_name()
BEGIN
    DECLARE local_variable_name INT;

    SELECT column_name FROM table_1 LIMIT 1 INTO local_variable_name;

    SELECT * FROM table_1;

    SELECT * FROM table_2;
END;;
DELIMITER ;
Related Question