处理表重复记录(查询和删除)

-- 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 #T
Go
Create table #T( [ ID ] int , [ Name ] nvarchar ( 1 ), [ Memo ] nvarchar ( 2 ))
Insert #T
select 1 ,N ' A ' ,N ' A1 ' union all
select 2 ,N ' A ' ,N ' A2 ' union all
select 3 ,N ' A ' ,N ' A3 ' union all
select 4 ,N ' B ' ,N ' B1 ' union all
select 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    A1
4           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    A3
5           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 #T
Go
Create table #T( [ ID ] int , [ Name ] nvarchar ( 1 ), [ Memo ] nvarchar ( 2 ))
Insert #T
select 1 ,N ' A ' ,N ' A1 ' union all
select 2 ,N ' A ' ,N ' A2 ' union all
select 3 ,N ' A ' ,N ' A3 ' union all
select 4 ,N ' B ' ,N ' B1 ' union all
select 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    A1
4           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    A3
5           B    B2

(2 行受影响)
*/





-- 3、删除重复记录没有大小关系时，处理重复值


-- > --> (Roy)生成測試數據

if not object_id ( ' Tempdb..#T ' ) is null
    drop table #T
Go
Create table #T( [ Num ] int , [ Name ] nvarchar ( 1 ))
Insert #T
select 1 ,N ' A ' union all
select 1 ,N ' A ' union all
select 1 ,N ' A ' union all
select 2 ,N ' B ' union all
select 2 ,N ' B '
Go

方法1:
if object_id ( ' Tempdb..# ' ) is not null
    drop table #
Select distinct * into # from #T -- 排除重复记录结果集生成临时表#

truncate table #T -- 清空表

insert #T select * from #    -- 把临时表#插入到表#T中

-- 查看结果
select * from #T

/*
Num         Name
----------- ----
1           A
2           B

(2 行受影响)
*/

-- 重新执行测试数据后用方法2
方法2:

alter table #T add ID int identity -- 新增标识列
go
delete a from   #T a where   exists ( select 1 from #T where Num = a.Num and Name = a.Name and ID > a.ID) -- 只保留一条记录
go
alter table #T drop column ID -- 删除标识列

-- 查看结果
select * from #T

/*
Num         Name
----------- ----
1           A
2           B

(2 行受影响)

*/

-- 重新执行测试数据后用方法3
方法3:
declare Roy_Cursor cursor local for
select count ( 1 ) - 1 ,Num,Name from #T group by Num,Name having count ( 1 ) > 1
declare @con int , @Num int , @Name nvarchar ( 1 )
open Roy_Cursor
fetch next from Roy_Cursor into @con , @Num , @Name
while @@Fetch_status = 0
begin
    set rowcount @con ;
    delete #T where Num = @Num and Name = @Name
    set rowcount 0 ;
    fetch next from Roy_Cursor into @con , @Num , @Name
end
close Roy_Cursor
deallocate Roy_Cursor

-- 查看结果
select * from #T
/*
Num         Name
----------- ----
1           A
2           B

(2 行受影响)
*/