CREATE TABLE `user` (
  `id` int(11) unsigned NOT NULL AUTO_INCREMENT COMMENT '自增id',
  `name` varchar(20) NOT NULL DEFAULT '' COMMENT '名字',
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

CREATE EVENT `delete_table_trigger`
ON SCHEDULE EVERY 1 SECOND STARTS '2000-01-01 00:00:00'
ON COMPLETION NOT PRESERVE
ENABLE
DO
delete from user where (select num from (select count(id) as num from user as tmp) as t)>100;