大家好，我是考100分的小小码 ，祝大家学习进步，加薪顺利呀。今天说一说MySQL中查询、删除重复记录的方法大全「建议收藏」,希望您对编程的造诣更进一步.
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：
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select title,count(*) as count from user_table group by title having count>1;
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SELECT * FROM t_info a WHERE ((SELECT COUNT(*) FROM t_info WHERE Title = a.Title) > 1) ORDER BY Title DESC
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一、查找重复记录
1、查找全部重复记录
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SELECT * FROM t_info a WHERE ((SELECT COUNT(*) FROM t_info WHERE Title = a.Title) > 1) ORDER BY Title DESC
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2、过滤重复记录(只显示一条)
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Select * From HZT Where ID In (Select Max(ID) From HZT Group By Title)
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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）
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Delete 表 Where 重复字段 In (Select 重复字段 From 表 Group By 重复字段 Having Count(*)>1)
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2、保留一条（这个应该是大多数人所需要的 ^_^）
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Delete HZT Where ID Not In (Select Max(ID) From HZT Group By Title)
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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
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select * from people where peopleId in (select peopleId from people group by peopleId having count(peopleId) > 1)
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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
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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)
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3、查找表中多余的重复记录（多个字段）
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select * from vitae a where (a.peopleId,a.seq) in (select peopleId,seq from vitae group by peopleId,seq having count(*) > 1)
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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
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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)
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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
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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)
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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
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select distinct * from tableName
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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
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select distinct * into #Tmp from tableName
drop table tableName
select * into tableName from #Tmp
drop table #Tmp
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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
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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)
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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/
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