SQL删除重复数据方法

数据库的小问题

（一）例如：id name value 1 a pp 2 a pp 3 b iii 4 b pp 5 b pp 6 c pp 7 c pp 8 c iii id是主键要求得到这样的结果id name value 1 a pp 3 b iii 4 b pp 6 c pp 8 c iii 方法1 delete YourTable where [id] not in ( select max([id]) from YourTable group by (name + value)) 方法2 delete a from 表 a left join( select id=min(id) from 表 group byname,value )b on a.id=b.id where b.id is null 查询及删除重复记录的SQL语句的步骤：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 frompeople 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 frompeople group by peopleId having count(peopleId) > 1) and rowid not in (select min(rowid) frompeople 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 (selectpeopleId,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 (selectpeopleId,seq from vitae group by peopleId,seq having count(*) > 1) and rowid not in (select min(rowid) fromvitae 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 (selectpeopleId,seq from vitae group by peopleId,seq having count(*) > 1) and rowid not in (select min(rowid) fromvitae group by peopleId,seq having count(*)>1) (二) 比方说在A表中存在一个字段“name”，而且不同记录之间的“name”值有可能会相同，现在就是需要查询出在该表中的各记录之间，“name”值存在重复的项；Select Name,Count(*) From A Group By NameHaving Count(*) > 1 如果还查性别也相同大则如下: Select Name,sex,Count(*) From A Group ByName,sex Having Count(*) > 1 (三) 方法一declare @max integer,@id integer declare cur_rows cursor local for select 主字段,count(*)from 表名 group by 主字段 having count(*) >； 1 open cur_rows fetch cur_rows into @id,@max while @@fetch_status=0 begin select @max = @max -1 set rowcount @max delete from 表名 where 主字段 = @id fetch cur_rows into @id,@max end close cur_rows set rowcount 0 方法二＂重复记录＂有两个意义上的重复记录，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 #Tmp2from #Tmp group by Name,autoID select * from #Tmp where autoID in(selectautoID 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）(四) 查询重复select * from tablename where id in ( select id from tablename group by id having count(id) > 1 )