关于SQL删除重复数据只保留一条

用SQL语句,删除掉重复项只保留一条 在几千条记录里,存在着些相同的记录,如何能用SQL语句,删除掉重复的呢 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   peopleName in (select peopleName    from people group by peopleName      having count(peopleName) > 1) and   peopleId not in (select min(peopleId) from people group by peopleName     having count(peopleName)>1) 3、删除表中多余的重复记录，重复记录是根据对个字段来判断的。并且重复条数多余2条。 while 1=1  begin     delete top (1) from CNLaw_Info     from CNLaw_Info p1 join ( select app_no,noticeDate,law_state,law_info from CNLaw_Info group by app_no,noticeDate,law_state     ,law_info having COUNT(*)>1 )      p2 on p1.app_no=p2.app_no and p1.noticeDate=p2.noticeDate and p1.law_state=p2.law_state and p1.law_info=p2.law_info      if @@ROWCOUNT=0 break; end; 上面这种方法效率非常的低，后来通过改进，例子如下： select  * from Patent.dbo.patent_US_Grant where ID in(select max(ID)    from Patent.dbo.patent_US_Grant where NoticeDate='20121023' group by ApplicationNumber having COUNT(ApplicationNumber)>1)   如果要删除的话把 “select *” 改为delete 解析上面语句：其实在sql server 最好用上 exists关键字，在这里的后面的select max(ID)。。。 ，查询出id最大的记录。 如果我们在查询时候，不用到having count 那么多个字段相同，找出重复数据的sql：  比如现在有一人员表  （表名：peosons） 若想将姓名、身份证号、住址这三个字段完全相同的记录查询出来：select p1.*  from persons  p1,persons p2 where p1.id<>p2.id and p1.cardid = p2.cardid  and p1.pname   = p2.pname and p1.address = p2.address 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)    6.消除一个字段的左边的第一位： update tableName set [Title]=Right([Title],(len([Title])-1)) where Title like '村%' 7.消除一个字段的右边的第一位： update tableName set [Title]=left([Title],(len([Title])-1)) where Title like '%村' 8.假删除表中多余的重复记录（多个字段），不包含rowid最小的记录 update vitae set ispass=-1 where peopleId in (select peopleId from vitae group by peopleId