DELETE e1 FROM EMPLOYEE e1, EMPLOYEE e2 WHERE e1.name = e2.name AND e1.id > e2.id;
ALTER TABLE `student` CHANGE `entry_date` `temp_entry_date` timestamp NOT NULL default '0000-00-00 00:00:00'; ALTER TABLE `student` ADD `entry_date` DATETIME NOT NULL default '0000-00-00 00:00:00'; UPDATE `student` SET `entry_date` = `temp_entry_date`; ALTER TABLE `student` DROP `temp_entry_date`;
INSERT INTO t1 (a,b,c) VALUES (1,2,3),(4,5,6) ON DUPLICATE KEY UPDATE c=VALUES(c); <insert id="insertOrUpdate"> INSERT INTO t1 (a,b,c) values <foreach collection="list" item="item" separator=","> (#{item.a},#{item.b},#{item.c}) </foreach> ON DUPLICATE KEY UPDATE c=values(c),b=values(b) </insert> long insertOrUpdate(List<Test> list);