MySQL 找出重复资料

MySQL 数据库出现重复资料时, 找出重复资料的方法有很多, 以下介绍两种常用的方法:

找出重复的纪录, 以 cid 字段作为判断, 会输出 cutomer_id 及出现次数:

SELECT cid, COUNT(*) FROM customer GROUP BY cid HAVING COUNT(*) > 1

不是显示出现次数, 而是将重复的资料全部输出:

select * from customer where
cid in (select cid from customer group by cid having count(cid) > 1)