How do you debug MySQL stored procedures?

Question

My current process for debugging stored procedures is very simple. I create a table called "debug" where I insert variable values from the stored procedure as it runs. This allows me to see the value of any variable at a given point in the script, but is there a better way to debug MySQL stored procedures?

Answer 1

The following debug_msg procedure can be called to simply output a debug message to the console:

DELIMITER $$

DROP PROCEDURE IF EXISTS `debug_msg`$$
DROP PROCEDURE IF EXISTS `test_procedure`$$

CREATE PROCEDURE debug_msg(enabled INTEGER, msg VARCHAR(255))
BEGIN
  IF enabled THEN
    select concat('** ', msg) AS '** DEBUG:';
  END IF;
END $$

CREATE PROCEDURE test_procedure(arg1 INTEGER, arg2 INTEGER)
BEGIN
  SET @enabled = TRUE;

  call debug_msg(@enabled, 'my first debug message');
  call debug_msg(@enabled, (select concat_ws('','arg1:', arg1)));
  call debug_msg(TRUE, 'This message always shows up');
  call debug_msg(FALSE, 'This message will never show up');
END $$

DELIMITER ;

Then run the test like this:

CALL test_procedure(1,2)

It will result in the following output:

** DEBUG:
** my first debug message
** DEBUG:
** arg1:1
** DEBUG:
** This message always shows up