Question

I currently have PHP code that handles the logic for this because I do not know how to handle it in SQL. I want to create a stored procedure that will delete all the rows except for the 5 newest for a given config_id. IE config_id = 5 gets passed to the SP so it knows which config_id it is looking to clean up.

CREATE TABLE  `TAA`.`RunHistory` (
  `id` int(11) NOT NULL auto_increment,
  `start_time` datetime default NULL,
  `stop_time` datetime default NULL,
  `success_lines` int(11) default NULL,
  `error_lines` int(11) default NULL,
  `config_id` int(11) NOT NULL,
  `file_id` int(11) NOT NULL,
  `notes` text NOT NULL,
  `log_file` longblob,
  `save` tinyint(1) NOT NULL default '0',
  PRIMARY KEY  (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=128 DEFAULT CHARSET=utf8;

Newest will be determined by start_time, if a stop_time is null but NOT the newest it should be deleted (stop_time can be null if a run was unceremoniously killed).

Answer 1

Here’s a procedure I tested on MySQL 5.1.46, but it uses no subqueries so you won’t get the error about no support for LIMIT in a subquery.

CREATE PROCEDURE DeleteBut5(IN c INT) BEGIN
  DECLARE i INT;
  DECLARE s DATETIME;

  SELECT id, stop_time INTO i, s
  FROM RunHistory WHERE config_id = c
  ORDER BY stop_time DESC, id DESC
  LIMIT 4, 1;

  DELETE FROM RunHistory WHERE stop_time < s OR stop_time = s AND id < i;
END

I recommend you create this covering index:

CREATE INDEX cov ON RunHistory (config_id, stop_time, id);