MySQL中查询、删除重复记录的⽅法⼤全
前⾔
本⽂主要给⼤家介绍了关于MySQL中查询、删除重复记录的⽅法，分享出来供⼤家参考学习，下⾯来看看详细的介绍：
查所有重复标题的记录：
select title,count(*) as count from user_table group by title having count>1;
SELECT * FROM t_info a WHERE ((SELECT COUNT(*) FROM t_info WHERE Title = a.Title) > 1) ORDER BY Title DESC
⼀、查重复记录
1、查全部重复记录
SELECT * FROM t_info a WHERE ((SELECT COUNT(*) FROM t_info WHERE Title = a.Title) > 1) ORDER BY Title DESC
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mysql删除重复的数据保留一条
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) 3、查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,s
eq 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)
总结
以上就是这篇⽂章的全部内容了，希望本⽂的内容对⼤家的学习或者⼯作能带来⼀定的帮助，如果有疑问⼤家可以留⾔交流，谢谢⼤家对的⽀持。

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