sql查询数据中重复记录并删除重复记录的方法总结

查找所有重复标题的记录：

    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 表 Where 重复字段 In (Select 重复字段 From 表 Group By 重复字段 Having Count(*)>1)  

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)