Sql Query to fetch highest marks - sql

Question

The table structure is like this:
Student (StudentID int, StudentName varchar(20))
Subject (SubjectID int, SubjectName varchar(20))
Score (ScoreID int, StudentID int, SubjectID int, Score int)
Here's the data
Student
| StudentID | StudentName |
| 1 | John |
| 2 | Nash |
| 3 | Albert |
---------------------------
Subject
| SubjectID | SubjectName |
| 1 | Maths |
| 2 | Physics |
| 3 | Chemistry|
| 4 | English |
---------------------------
Score
| ScoreID | StudentID | SubjectID | Score |
| 1 | 1 | 1 | 34 |
| 2 | 1 | 2 | 45 |
| 3 | 1 | 3 | 56 |
| 4 | 2 | 1 | 78 |
| 5 | 2 | 3 | 23 |
| 6 | 2 | 4 | 44 |
| 7 | 3 | 1 | 45 |
| 8 | 3 | 2 | 10 |
| 9 | 3 | 3 | 54 |
| 10 | 3 | 4 | 74 |
-------------------------------------------
Output:
|StudentName | Score | SubjectName |
| John | 45 | Physics |
| John | 56 | Chemistry |
| Nash | 78 | Maths |
| Albert | 74 | English |
------------------------------------
I want to write a query to fetch the top scorer of every subject along with their scores and subject names, without using Row_Number(), Rank() and Dense_Rank().
I've written this query, but I think it can be improved:
select
st.StudentName, Score, B.SubjectID
from
(select
StudentID, Sc.SubjectID, Sc.Score
from
(select
SubjectID, MAX(Score) as 'Score'
from
Score Sc
inner join
subject sb on sc.subjectid = sb.subjectid
group by
SubjectID) A
inner join
score sc on sc.SubjectID = a.SubjectID and sc.Score = A.Score) B
inner join
Student st on st.studentID = B.StudentID

Answer 1

This is a solution without using RANK or ROW_NUMBER. Also this is much simplified to meet your output. Hope it helps
SELECT st.StudentName ,s.Score ,su.SubjectName FROM (SELECT
SubjectID,MAX(Score) as Max FROM Score GROUP BY SubjectID) a
INNER JOIN Score s on a.SubjectID=s.SubjectID AND a.MAX=s.Score
INNER JOIN Student st on s.StudentID=st.StudentID
INNER JOIN Subject su on s.SubjectID=su.SubjectID

Answer 2

You would use the ANSI standard rank() or row_number() functions. Assuming you want all duplicates, use rank():
select StudentName, SubjectName, Score
from (select st.StudentName, su.SubjectName, s.Score,
rank() over (partition by su.SubjectName order by s.Score desc) as seqnum
from score s join
student st
on s.studentid = st.studentid join
subject su
on s.subjectid = su.subjectid
) s
where seqnum = 1;
If you wanted exactly one row per subject with an arbitrary top student, use row_number().
In SQL Server, you can also do this without a subquery:
select top (1) with ties st.StudentName, su.SubjectName, s.Score
from score s join
student st
on s.studentid = st.studentid join
subject su
on s.subjectid = su.subjectid
order by rank() over (partition by su.SubjectName order by s.Score desc)
Another fun option is apply -- and this doesn't use window functions and can have quite good performance:
select ss.StudentName, su.SubjectName, ss.Score
from subject su cross apply
(select top (1) with ties s.*
from score s join
student st
on s.studentid = st.studentid join
where s.subjectid = su.subjectid
order by su.score desc
) ss;

Answer 3

You can use ROW_NUMBER like below
SELECT * FROM
(SELECT st.StudentName, sub.SubjectName, s.Score,
ROW_NUMBER() OVER(partition by sub.SubjectName order by s.Score Desc) as row_no
FROM Score s
LEFT OUTER JOIN Student st on s.StudentID = st.StudentID
LEFT OUTER JOIN Subject sub on s.SubjectID = sub.SubjectID) as tblMain
WHERE row_no = 1