--参考--处理表重复记录(查询和删除)/******************************************************************************************************************************************************1、Num、Name相同的重复值记录,没有大小关系只保留一条2、Name相同,ID有大小关系时,保留大或小其中一个记录整理人：中国风(Roy)
日期:2008.06.06******************************************************************************************************************************************************/
--1、用于查询重复处理记录(如果列没有大小关系时2000用生成自增列和临时表处理,SQL2005用row_number函数处理)
--> --> (Roy)生成測試數據 if not object_id('Tempdb..#T') is null drop table #TGoCreate table #T([ID] int,[Name] nvarchar(1),[Memo] nvarchar(2))Insert #Tselect 1,N'A',N'A1' union allselect 2,N'A',N'A2' union allselect 3,N'A',N'A3' union allselect 4,N'B',N'B1' union allselect 5,N'B',N'B2'Go
--I、Name相同ID最小的记录(推荐用1,2,3),方法3在SQl05时，效率高于1、2方法1:Select * from #T a where not exists(select 1 from #T where Name=a.Name and ID<a.ID)
方法2:select a.* from #T a join (select min(ID)ID,Name from #T group by Name) b on a.Name=b.Name and a.ID=b.ID
方法3:select * from #T a where ID=(select min(ID) from #T where Name=a.Name)
方法4:select a.* from #T a join #T b on a.Name=b.Name and a.ID>=b.ID group by a.ID,a.Name,a.Memo having count(1)=1
方法5:select * from #T a group by ID,Name,Memo having ID=(select min(ID)from #T where Name=a.Name)
方法6:select * from #T a where (select count(1) from #T where Name=a.Name and ID<a.ID)=0
方法7:select * from #T a where ID=(select top 1 ID from #T where Name=a.name order by ID)
方法8:select * from #T a where ID!>all(select ID from #T where Name=a.Name)
方法9(注:ID为唯一时可用):select * from #T a where ID in(select min(ID) from #T group by Name)
--SQL2005:
方法10:select ID,Name,Memo from (select *,min(ID)over(partition by Name) as MinID from #T a)T where ID=MinID
方法11:
select ID,Name,Memo from (select *,row_number()over(partition by Name order by ID) as MinID from #T a)T where MinID=1
生成结果:/*ID Name Memo----------- ---- ----1 A A14 B B1
(2 行受影响)*/
--II、Name相同ID最大的记录,与min相反:方法1:Select * from #T a where not exists(select 1 from #T where Name=a.Name and ID>a.ID)
方法2:select a.* from #T a join (select max(ID)ID,Name from #T group by Name) b on a.Name=b.Name and a.ID=b.ID order by ID
方法3:select * from #T a where ID=(select max(ID) from #T where Name=a.Name) order by ID
方法4:select a.* from #T a join #T b on a.Name=b.Name and a.ID<=b.ID group by a.ID,a.Name,a.Memo having count(1)=1
方法5:select * from #T a group by ID,Name,Memo having ID=(select max(ID)from #T where Name=a.Name)
方法6:select * from #T a where (select count(1) from #T where Name=a.Name and ID>a.ID)=0
方法7:select * from #T a where ID=(select top 1 ID from #T where Name=a.name order by ID desc)
方法8:select * from #T a where ID!<all(select ID from #T where Name=a.Name)
方法9(注:ID为唯一时可用):select * from #T a where ID in(select max(ID) from #T group by Name)
--SQL2005:
方法10:select ID,Name,Memo from (select *,max(ID)over(partition by Name) as MinID from #T a)T where ID=MinID
方法11:select ID,Name,Memo from (select *,row_number()over(partition by Name order by ID desc) as MinID from #T a)T where MinID=1
生成结果2:/*ID Name Memo----------- ---- ----3 A A35 B B2
(2 行受影响)*/
--2、删除重复记录有大小关系时,保留大或小其中一个记录
--> --> (Roy)生成測試數據
if not object_id('Tempdb..#T') is null drop table #TGoCreate table #T([ID] int,[Name] nvarchar(1),[Memo] nvarchar(2))Insert #Tselect 1,N'A',N'A1' union allselect 2,N'A',N'A2' union allselect 3,N'A',N'A3' union allselect 4,N'B',N'B1' union allselect 5,N'B',N'B2'Go
--I、Name相同ID最小的记录(推荐用1,2,3),保留最小一条方法1:delete a from #T a where exists(select 1 from #T where Name=a.Name and ID<a.ID)
方法2:delete a from #T a left join (select min(ID)ID,Name from #T group by Name) b on a.Name=b.Name and a.ID=b.ID where b.Id is null
方法3:delete a from #T a where ID not in (select min(ID) from #T where Name=a.Name)
方法4(注:ID为唯一时可用):delete a from #T a where ID not in(select min(ID)from #T group by Name)
方法5:delete a from #T a where (select count(1) from #T where Name=a.Name and ID<a.ID)>0
方法6:delete a from #T a where ID<>(select top 1 ID from #T where Name=a.name order by ID)
方法7:delete a from #T a where ID>any(select ID from #T where Name=a.Name)
select * from #T
生成结果:/*ID Name Memo----------- ---- ----1 A A14 B B1
(2 行受影响)*/
--II、Name相同ID保留最大的一条记录:
方法1:delete a from #T a where exists(select 1 from #T where Name=a.Name and ID>a.ID)
方法2:delete a from #T a left join (select max(ID)ID,Name from #T group by Name) b on a.Name=b.Name and a.ID=b.ID where b.Id is null
方法3:delete a from #T a where ID not in (select max(ID) from #T where Name=a.Name)
方法4(注:ID为唯一时可用):delete a from #T a where ID not in(select max(ID)from #T group by Name)
方法5:delete a from #T a where (select count(1) from #T where Name=a.Name and ID>a.ID)>0
方法6:delete a from #T a where ID<>(select top 1 ID from #T where Name=a.name order by ID desc)
方法7:delete a from #T a where ID<any(select ID from #T where Name=a.Name)
select * from #T/*ID Name Memo----------- ---- ----3 A A35 B B2
(2 行受影响)*/
