sql 查询重复记录（mysql）

1、单子段（nick_name）

查询所有有重复记录的所有记录

select * from user where nick_name in (select nick_name from user group by nick_name having count(nick_name)>1);

查询出有重复记录的各个记录组中的ID最大的记录

select * from user where id in (select max(id) from user group by nick_name having count(nick_name)>1);

查询出多余的记录，不查出id最小的记录

select * from user where id in (select max(id) from user group by nick_name having count(nick_name)>1);

删除多余的重复记录，只保留id 最小的记录

delete from user where nick_name in (select nick_name from (select nick_name from user group by nick_name having count(nick_name)>1) as tmp1) and id not in (select id from (select min(id) from user group by nick_name having count(nick_name)>1) as tmp2);

2、对字段

查出所有有重复记录的记录

select * from user where (nick_name,password) in (select nick_name,password from user group by nick_name,password where having count(nick_name)>1);

查出有重复记录的各个记录组中ID最大的记录

select * from user where id in (select max(id) from user group by nick_name,password where having count(nick_name)>1);

查处各个重复记录组中多余的鸡柳数据，不查出id最小的一条

select * from user where (nick_name,password) in (select nick_name,password from user group by nick_name,password having count(nick_name)>1) and id not in (select min(id) from user group by nick_name,password having count(nick_name)>1);

删除多有的重复记录，只保留id最小的记录】

delete from user where (nick_name,password) in (select nick_name,password from (select nick_name,password from user group by nick_name,password having count(nick_name)>1) as tmp1) and id not in (select id from (select min(id) id from user group by nick_name,password having count(nick_name)>1) as tmp2);