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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：
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、查找重复记录
1、查找全部重复记录
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
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
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、查找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、查找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,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
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
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