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mysql怎么查询和删除重复记录

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文章目录
  1. 查找重复记录
  2. 删除重复记录
  3. 举例
  4. 补充

查找所有重复标题的记录:

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

查找重复记录

查找全部重复记录

  1. Select * FromWhere 重复字段 In (Select 重复字段 FromGroup By 重复字段 Having Count(*)>1)

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

删除重复记录

删除全部重复记录(慎用)

  1. DeleteWhere 重复字段 In (Select 重复字段 FromGroup By 重复字段 Having Count(*)>1)

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

举例

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)

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)

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)

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)

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)

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。

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. select distinct * into #Tmp from tableName
  2. drop table tableName
  3. select * into tableName from #Tmp
  4. 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。

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

原文:http://blog.csdn.net/l1028386804/article/details/51733585

来源:本文由思享SEO博客原创撰写,欢迎分享本文,转载请保留出处和链接!

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