sql查询重复记录方法大全

sql查询重复记录方法大全 
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


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)




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)






最后一个select即得到了Name，Address不重复的结果集（但多了一个autoID字段，实际写时可以写在select子句中省去此列