[转]MySQL删除重复数据, 去重分析

查找所有重复标题的记录：

SELECT * FROM t_info a WHERE ((SELECT COUNT(*) FROM t_info WHERE Title = a.Title) > 1) ORDER BY Title DESC

一、查找重复记录

1、查找全部重复记录

Select * From 表 Where 重复字段 In (Select 重复字段 From 表 Group By 重复字段 Having Count(*)>1)

2、过滤重复记录(只显示一条)

Select * From HZT Where ID In (Select Max(ID) From HZT Group By Title)

注：此处显示ID最大一条记录 二、删除重复记录 1、删除全部重复记录（慎用）

Delete 表 Where 重复字段 In (Select 重复字段 From 表 Group By 重复字段 Having Count(*)>1)

2、保留一条（这个应该是大多数人所需要的 ^_^）

Delete HZT Where ID Not In (Select Max(ID) From HZT Group By Title)

注：此处保留ID最大一条记录 三、举例 1、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

select * from people where peopleId in (select peopleId from people group by peopleId having count(peopleId) > 1)

2、删除表中多余的重复记录，重复记录是根据单个字段（peopleId）来判断，只留有rowid最小的记录

delete from people where peopleId in (select peopleId from people group by peopleId having count(peopleId) > 1) and rowid not in (select min(rowid) from people group by peopleId having count(peopleId )>1)

实际测试, 这里会报错, 需要给 in 和 not in 的select结果起个别名, 下面是我实际测试可行的sql语句, 在t_users表中给wx_openid字段去重, 保留id最小的一条记录:

delete from t_users where wx_openid in (SELECT wx_openid FROM ((select wx_openid from t_users group by wx_openid having count(wx_openid) > 1)) tmp) and id not in ( SELECT id FROM (select min(id) as id from t_users group by wx_openid having count(wx_openid )>1) tmp2)

3、查找表中多余的重复记录（多个字段）

 select * from vitae a where (a.peopleId,a.seq) in (select peopleId,seq from vitae group by peopleId,seq having count(*) > 1)

4、删除表中多余的重复记录（多个字段），只留有rowid最小的记录

 delete from vitae a where (a.peopleId,a.seq) in (select peopleId,seq from vitae group by peopleId,seq having count(*) > 1) and rowid not in (select min(rowid) from vitae group by peopleId,seq having count(*)>1)

5、查找表中多余的重复记录（多个字段），不包含rowid最小的记录

 select * from vitae a where (a.peopleId,a.seq) in (select peopleId,seq from vitae group by peopleId,seq having count(*) > 1) and rowid not in (select min(rowid) from vitae group by peopleId,seq having count()>1)

四、补充 有两个以上的重复记录，一是完全重复的记录，也即所有字段均重复的记录，二是部分关键字段重复的记录，比如Name字段重复，而其他字段不一定重复或都重复可以忽略。 1、对于第一种重复，比较容易解决，使用

select distinct * from tableName

就可以得到无重复记录的结果集。 如果该表需要删除重复的记录（重复记录保留1条），可以按以下方法删除

select distinct * into #Tmp from tableName
drop table tableName
select * into tableName from #Tmp
drop table #Tmp

发生这种重复的原因是表设计不周产生的，增加唯一索引列即可解决。 2、这类重复问题通常要求保留重复记录中的第一条记录，操作方法如下 假设有重复的字段为Name,Address，要求得到这两个字段唯一的结果集

select identity(int,1,1) as autoID, * into #Tmp from tableName
select min(autoID) as autoID into #Tmp2 from #Tmp group by Name,autoID
select * from #Tmp where autoID in(select autoID from #tmp2)

原文链接：https://blog.csdn.net/l1028386804/article/details/51733585