刪除重復(fù)記錄有大小關(guān)系時(shí),保留大或小其中一個(gè)記錄

--> --> (Roy)生成測(cè)試數(shù)據(jù)

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最小的記錄(推薦用1,2,3),保留最小一條
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為唯一時(shí)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

生成結(jié)果:
/*
ID Name Memo
----------- ---- ----
1 A A1
4 B B1

(2 行受影響)
*/


--II、Name相同ID保留最大的一條記錄:
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為唯一時(shí)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 行受影響)
*/


--3、刪除重復(fù)記錄沒(méi)有大小關(guān)系時(shí)，處理重復(fù)值
--> --> (Roy)生成測(cè)試數(shù)據(jù)

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--排除重復(fù)記錄結(jié)果集生成臨時(shí)表#
truncate table #T--清空表
insert #T select * from # --把臨時(shí)表#插入到表#T中

--查看結(jié)果
select * from #T

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

(2 行受影響)
*/

--重新執(zhí)行測(cè)試數(shù)據(jù)后用方法2
方法2:
alter table #T add ID int identity--新增標(biāo)識(shí)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)--只保留一條記錄
go
alter table #T drop column ID--刪除標(biāo)識(shí)列

--查看結(jié)果
select * from #T

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

(2 行受影響)

*/

--重新執(zhí)行測(cè)試數(shù)據(jù)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

--查看結(jié)果
select * from #T
/*
Num Name
----------- ----
1 A
2 B

(2 行受影響)
*/ 

總結(jié)

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