MySQL 数据查重、去重的实现语句

有一个表user，字段分别有id、nick_name、password、email、phone。

一、单字段（nick_name）

查出所有有重复记录的所有记录

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1	select * from user where nick_name in ( select nick_name from user group by nick_name 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

?

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

查出多余的记录，不查出id最小的记录

?

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);

删除多余的重复记录，只保留id最小的记录

?

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);

二、多字段（nick_name,password）

查出所有有重复记录的记录

?

1	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

?

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

查出各个重复记录组中多余的记录数据，不查出id最小的一条

?

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);

删除多余的重复记录，只保留id最小的记录

?

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);

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原文链接：https://www.addcoder.com/blog/article_detail/edbhoezw/