Question

Consider the following table:

CREATE TABLE `prize` (
  `id` bigint(20) NOT NULL AUTO_INCREMENT,
  `prize_details_id` bigint(20) NOT NULL,
  `status` tinyint(4) DEFAULT '0',
  `available_at` datetime DEFAULT NULL,
  PRIMARY KEY (`id`),
  KEY `prize_details_id_idx` (`prize_details_id`),
  KEY `status_idx` (`status`),
  KEY `available_at_idx` (`available_at`),
  CONSTRAINT `prize_prize_details_id_prize_detail_id` FOREIGN KEY (`prize_details_id`) REFERENCES `prize_detail` (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=1611419 DEFAULT CHARSET=latin1;

What I’d like to do is delete n records, where n is the total number of records that match a condition less 20. The table is reasonably big (greater than 1m records).

The condition is a complex one that involves a relative date query on frequently changing data, and involves a join on a couple of other tables too, so first selecting how many there are that match the condition and then deleting twenty fewer isn’t going to work as far as I know.

The condition is all of the following:

• prize_details_id is x (need to run the same query for a few different IDs)
• available_at is null
• prize_id doesn’t exist in another table
• status is 1
• tier (on the prize_detail table) is above y

Answer 1

Maybe like this:

• create a temporary table _tmp (id int auto_increment, prize_id int)
• select matching prize ids into this temporary table
• delete from prize where id in (select prize_id from _tmp where id >=20)