mysql数据库如何去除重复数据-木庄网络博客

2022-02-14 18:09:02 PHP中文网数据库百度已收录

本文摘自PHP中文网，作者coldplay.xixi，侵删。

mysql数据库去除重复数据的方法：1、查询需要删除的记录，会保留一条记录；2、删除重复记录，只保留一条记录，代码为【delete a from test1 a, (...)as bid from test1 c where..】。

mysql数据库去除重复数据的方法：

1、查询需要删除的记录，会保留一条记录。

1	`select a.id,a.subject,a.RECEIVER from test1 a left join (select c.subject,c.RECEIVER ,max(c.id)` `as` `bid from test1 c where status=0 GROUP BY RECEIVER,SUBJECT having` `count(1) >1) b on a.id< b.bid where a.subject=b.subject` `and` `a.RECEIVER = b.RECEIVER` `and` `a.id < b.bid`

2、删除重复记录，只保留一条记录。注意，subject,RECEIVER 要索引，否则会很慢的。

1	`delete` `a from test1 a, (select c.subject,c.RECEIVER ,max(c.id)` `as` `bid from test1 c where status=0 GROUP BY RECEIVER,SUBJECT having` `count(1) >1) b where a.subject=b.subject` `and` `a.RECEIVER = b.RECEIVER` `and` `a.id < b.bid;`

3、查找表中多余的重复记录，重复记录是根据单个字段（peopleId）来判断