刪除重復記錄有大小關系時,保留大或小其中一個記錄

--> --> (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)