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：
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| 1 | select title, count (*) as count from user_table group by title having count >1; |
| 1 | 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
| 1 | 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)
| 1 | 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）
| 1 | 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 ^_^）
| 1 | 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
| 1 | 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
| 1 | 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、查找表中多余的重复记录（多个字段）
| 1 | 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
| 1 | 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
| 1 | 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
| 1 | 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
| 1 2 3 4 | 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
| 1 2 3 | 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
原文链接：http://blog.phpsoho.com/2017/06/20/mysql之-查询重复记录、删除重复记录方法大全/
,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：
查找所有重复标题的记录：
| 1 | select title, count (*) as count from user_table group by title having count >1; |
| 1 | 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
| 1 | 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)
| 1 | 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）
| 1 | 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 ^_^）
| 1 | 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
| 1 | 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
| 1 | 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、查找表中多余的重复记录（多个字段）
| 1 | 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
| 1 | 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
| 1 | 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
| 1 | 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
| 1 2 3 4 | 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
| 1 2 3 | 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
原文链接：http://blog.phpsoho.com/2017/06/20/mysql之-查询重复记录、删除重复记录方法大全/
