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

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

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

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);

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);
 

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

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);

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);