求SQL语句(最早时间记录)

--处理表重复记录(查询和删除)

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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

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--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

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'

--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

Select * from #T a where not exists(select 1 from #T where Name=a.Name and ID<a.ID)

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

select * from #T a where ID=(select min(ID) from #T where Name=a.Name)

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 

select * from #T a group by ID,Name,Memo having ID=(select min(ID)from #T where Name=a.Name)

select * from #T a where (select count(1) from #T where Name=a.Name and ID<a.ID)=0

select * from #T a where ID=(select top 1 ID from #T where Name=a.name order by ID)

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)