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Õâ¸öSQLÓï¾äÔõôд?
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ѧÉúID(sid)¿Î³Ì(cName)³É¼¨(score)
1 1 75
2 2 90
3 2 60
4 3 89
5 3 80
6 3 70
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SQL code:

select k.*
from (select sid,
cname,
score,
rank() over(partition by cname order by score desc) rn
from t) k
where k.rn <= 2

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SQL code:
select m.* from
(
select t.* , row_number() over(partition by cName order by score desc) px from tb t
) m
where px <= 2

select m.* from
(
select t.* , (select count(1) from tb where cName = t.cName and score > t.score) + 1 from tb t
) m
where px <= 2

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select id,cname from 
  (select id,cname,rank () over (partition by cname order by score desc) rk
  from t)
where rk<=2;

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SQL code:

SQL>
SQL> with t as (
2 select 1 sid, 1 cname, 75 score from dual union all
3 select 2, 2, 90 from dual union all
4 select 3, 2, 60 from dual union all
5 select 4, 3, 89 from dual union all