这个怎么实现的？
CREATE TABLE hard (qu char (11) ,co char (11) ,je numeric(3, 0)) 
insert into hard values ('A','1',3)
insert into hard values ('A','2',4)
insert into hard values ('A','4',2)
insert into hard values ('A','6',9)
insert into hard values ('B','1',4)
insert into hard values ('B','2',5)
insert into hard values ('B','3',6)
insert into hard values ('C','3',4)
insert into hard values ('C','6',7)
insert into hard values ('C','2',3)
要求查询出来的结果如下：
 
qu co je 
----------- ----------- ----- 
A 6 9
A 2 4
B 3 6
B 2 5
C 6 7
C 3 4


------解决方案--------------------
select * from hard a
where je in(select top 2 je from hard where qu=a.qu order by je desc)
order by qu,je desc
------解决方案--------------------

探讨

select * from hard a
where je in(select top 2 je from hard where qu=a.qu order by je desc)
order by qu,je desc
这个子查询是什么意思呀？