Sql query for Top N rows using a group by

Question

Hi i tried many ways to solve this but missing some thing.. I have two tables Student and Score

Sid Cid Score
6   1   90
1   1   80
4   1   80
3   1   70
2   1   60
6   2   80
1   2   70
2   2   60
4   2   60
5   2   50
4   3   80
7   3   80
6   3   70
8   3   60
2   3   50

Sid Sname Sbday   Ssex
1   As  1980    female
2   Al  1986    male
3   An  1989    male
4   ja  1986    male
5   ma  1983    female
6   phi 1986    male
7   Geo 1993    male
8   lil 1990    female
9   cha 1993    male

I need to Return Sid and Sname of the students who have the top 2 highest score for each course. If existed, return Sid and Sname of the student who has the highest score among all the male students for each course.

Here top 2 highest score is not just top two records in a group for ex : top 2 highest score in 1st group is 90, 80 ,80 .

I need out put like this

Sid Cid Score
6    1   90
1    1   80
4    1   80
6    2   80
1    2   70
2    2   60
4    2   60
4    3   80
7    3   80
6    3   70

I tried the following code :

select A.Sid , S.SNAME, Score,Cid
   from Score a,STUDENTS S
    where 2 >(select count(Cid)
               from Score
              where Cid=a.Cid
                and Score>a.Score)
    AND A.SID = S.SID
    order by Cid,Score desc

Answer 1

For the first question (list the students who have the top 2 highest score for each course), you should try this:

SELECT SC.Sid , ST.SNAME, SC.Score, SC.Cid 
FROM (  SELECT *, DENSE_RANK() OVER(PARTITION BY Cid ORDER BY Score DESC) TopScore
        FROM Score) AS SC
INNER JOIN Students AS ST
ON SC.Sid = ST.Sid
WHERE SC.TopScore <= 2

For your second quetion (the student who has the highest score among all the male students for each course), do the following:

SELECT A.Sid , A.SNAME, A.Score, A.Cid 
FROM (  SELECT SC.Sid , ST.SNAME, SC.Score, SC.Cid, DENSE_RANK() OVER(PARTITION BY Cid ORDER BY Score DESC) TopScore
        FROM Score AS SC
        INNER JOIN Students AS ST
        ON SC.Sid = ST.Sid
        WHERE ST.Ssex = 'male') A
WHERE A.TopScore = 1 

Hope it helps.