Sum of Highest 5 numbers in SQL Server 2000 - sql

Question

I am having a problem in query some data from database. My table is given below:
What i need is that sum of 5 highest total_marks from the table for each student.
Although i tried the code given below, but it is not returning what i expected.
SELECT s.studentid, SUM(s.total_marks)
FROM students s
WHERE s.sub_code IN (SELECT TOP 5 sub_code
FROM students a
WHERE a.studentid = s.studentid
ORDER BY total_marks DESC)
GROUP BY studentid
Please help me guys. Thanking you advance.

Answer 1

You query could work if there's unique/primary key on (studentId, subcode). At the moment, the query returns 6 records instead of 5 for studentId = 1, for example, beause of duplicate subcode 303.
Usually table should have a unique key, may be you can add incremental id to rewrite your query like:
select s.*
from students as s
where
s.id in (
select top 5 a.id
from students as a
where a.studentId = s.studentId
order by a.total_marks desc
);
Or, if you have unique combinations of (studentId, subcode, total_marks), you can use query like this:
select s.*
from students as s
where
exists (
select *
from (
select top 5 a.subcode, a.total_marks
from students as a
where a.studentId = s.studentId
order by a.total_marks desc
) as b
where b.subcode = s.subcode and b.total_marks = s.total_marks
);
sql fiddle demo

Answer 2

First you should select top 5 grades for each student -
select row_number() over (partition by studentid order by total_marks desc) as rank,
studentid,
total_marks
from students
where rank <= 5
from there you'll be able to use this as a subquery, and use group_by and sum:
select studentid, sum(total_marks)
from
(
select row_number() over (partition by studentid order by total_marks desc) as rank,
studentid,
total_marks
from students
where rank <= 5
) t
group by studentid

Answer 3

This isn't ideal, but the method you started to use requires a primary key column. You can simulate one with a temp table since SQL 2000.
CREATE TABLE #temp (
StudentID INT,
total_marks INT,
ID INT Identity(1,1)
)
INSERT INTO #temp (
StudentID,
total_Marks
)
Select
StudentID,
total_marks
FROM Students
SELECT s.studentid, SUM(s.total_marks)
FROM #temp s
WHERE s.ID IN (SELECT TOP 2
a.ID
FROM #temp a
WHERE a.studentid = s.studentid
ORDER BY total_marks DESC)
GROUP BY studentid
I think SQL 2000 may have a slightly more compact syntax for this, but SQL Fiddle won't let me test versions that old.
Please test this carefully. You will be dumping this entire table to a temp table and that's almost always a bad idea.
Also, ensure that there is some combination of fields not including the total that uniquely identifies a row, or consider adding a surrogate key column to the table.
SQL Fiddle Demo