求SQL分组中取最大值后的那条记录
表结构为：
ID sub_ID RQ
1 1 2012-1-1
1 2 2012-9-2
1 3 2012-1-3
2 1 2012-5-6
2 2 2012-1-2
3 1 2012-10-1
3 2 2012-1-2
3 3 2012-1-5
3 4 2012-11-9
需要用一个SQL语句得到：
ID sub_ID RQ
1 2 2012-9-2
2 1 2012-5-6
3 4 2012-11-9
怎么写SQL语句呢？
[解决办法]
--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)*/--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 #TGoCreate table #T([Num] int,[Name] nvarchar(1))Insert #Tselect 1,N'A' union allselect 1,N'A' union allselect 1,N'A' union allselect 2,N'B' union allselect 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 A2 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godelete 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goalter table #T drop column ID--删除标识列--查看结果select * from #T/*Num Name----------- ----1 A2 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 forselect count(1)-1,Num,Name from #T group by Num,Name having count(1)>1declare @con int,@Num int,@Name nvarchar(1)open Roy_Cursorfetch next from Roy_Cursor into @con,@Num,@Namewhile @@Fetch_status=0begin set rowcount @con; delete #T where Num=@Num and Name=@Name set rowcount 0; fetch next from Roy_Cursor into @con,@Num,@Nameendclose Roy_Cursordeallocate Roy_Cursor--查看结果select * from #T/*Num Name----------- ----1 A2 B(2 行受影响)*/
[解决办法]
/*
ID sub_ID RQ
1 1 2012-1-1
1 2 2012-9-2
1 3 2012-1-3
2 1 2012-5-6
2 2 2012-1-2
3 1 2012-10-1
3 2 2012-1-2
3 3 2012-1-5
3 4 2012-11-9
需要用一个SQL语句得到：
ID sub_ID RQ
1 2 2012-9-2
2 1 2012-5-6
3 4 2012-11-9
怎么写SQL语句呢？
*/
go
if OBJECT_ID( 'tbl ')is not null
drop table tbl
go
create table tbl(
ID int,
sub_ID int,
RQ date
)
go
insert tbl
select 1,1, '2012-1-1 ' union all
select 1,2, '2012-9-2 ' union all
select 1,3, '2012-1-3 ' union all
select 2,1, '2012-5-6 ' union all
select 2,2, '2012-1-2 ' union all
select 3,1, '2012-10-1 ' union all
select 3,2, '2012-1-2 ' union all
select 3,3, '2012-1-5 ' union all
select 3,4, '2012-11-9 '
--方法一:
select ID,sub_ID,RQ from
(select *,row_number()over(partition by ID order by RQ desc) as num from tbl)a where num=1
--方法二:
select a.ID,sub_ID,a.RQ from tbl
inner join
(select ID,max(RQ) as RQ from tbl group by ID)a
on a.ID=tbl.ID and a.RQ=tbl.RQ
--方法三:
select *from tbl a where RQ in(select max(RQ) from tbl b where a.ID=b.ID)
/*
结果:
IDsub_IDRQ
122012-09-02
212012-05-06
342012-11-09
*/
[解决办法]
用RANK（）函数..不是说日期有可能重复么..最大的日期并且相同的 会排同一个位置