Mysql必读MySQL中查询、删除重复记录的方法大全
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《Mysql必读MySQL中查询、删除重复记录的方法大全》要点： MYSQL应用前言 MYSQL应用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： MYSQL应用查找所有重复标题的记录： MYSQL应用
select title,count(*) as count from user_table group by title having count>1;
MYSQL应用
SELECT * FROM t_info a WHERE ((SELECT COUNT(*) FROM t_info WHERE Title = a.Title) > 1) ORDER BY Title DESC
MYSQL应用一、查找重复记录 MYSQL应用1、查找全部重复记录 MYSQL应用
SELECT * FROM t_info a WHERE ((SELECT COUNT(*) FROM t_info WHERE Title = a.Title) > 1) ORDER BY Title DESC
MYSQL应用2、过滤重复记录(只显示一条) MYSQL应用
Select * From HZT Where ID In (Select Max(ID) From HZT Group By Title)
MYSQL应用注：此处显示ID最大一条记录 MYSQL应用二、删除重复记录 MYSQL应用1、删除全部重复记录(慎用) MYSQL应用
Delete 表 Where 重复字段 In (Select 重复字段 From 表 Group By 重复字段 Having Count(*)>1)
MYSQL应用2、保留一条(这个应该是大多数人所需要的 ^_^) MYSQL应用
Delete HZT Where ID Not In (Select Max(ID) From HZT Group By Title)
MYSQL应用注：此处保留ID最大一条记录 MYSQL应用三、举例 MYSQL应用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 MYSQL应用
select * from people where peopleId in (select peopleId from people group by peopleId having count(peopleId) > 1)
MYSQL应用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 MYSQL应用
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)
MYSQL应用3、查找表中多余的重复记录(多个字段) MYSQL应用
select * from vitae a where (a.peopleId,a.seq) in (select peopleId,seq from vitae group by peopleId,seq having count(*) > 1)
MYSQL应用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 MYSQL应用
delete from vitae a where (a.peopleId,seq having count(*) > 1) and rowid not in (select min(rowid) from vitae group by peopleId,seq having count(*)>1)
MYSQL应用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 MYSQL应用
select * from vitae a where (a.peopleId,seq having count(*)>1)
MYSQL应用四、补充 MYSQL应用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. MYSQL应用1、对于第一种重复,比较容易解决,使用 MYSQL应用
select distinct * from tableName
MYSQL应用就可以得到无重复记录的结果集. MYSQL应用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 MYSQL应用
select distinct * into #Tmp from tableName
drop table tableName
select * into tableName from #Tmp
drop table #Tmp
MYSQL应用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. MYSQL应用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 MYSQL应用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 MYSQL应用
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)
MYSQL应用总结 MYSQL应用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,谢谢大家对编程之家PHP的支持. （编辑：李大同） 【声明】本站内容均来自网络，其相关言论仅代表作者个人观点，不代表本站立场。若无意侵犯到您的权利，请及时与联系站长删除相关内容! |