row_number() and partition

[quote]一个表有三列，id，name，score，现在要取得每个人分数最高的两门课程[/quote]

create temp table tmp_xxx
as
select 1 id,'A' name,80 grade
UNION ALL
select 2,'A',90
UNION ALL
select 3,'A',60
UNION ALL
select 4,'B',100
UNION ALL
select 5,'B',90
UNION ALL
select 6,'B',50;


select id,name,grade
from 
(
select id,name,grade, row_number() over (partition by name order by grade desc) as RN
from
tmp_xxx
) tmp
where RN<=2;