Question

I have a table with 3 fields like this:

ProfessorID    StudentID    Mark P1             S1              9 P1             S2              8 P1             S3             10 P2             S1              7 P2             S2              2 P2             S3              4 P3             S4              5 P4             S1              6 

A professor can teach many students, and vice versa, a student can learn from many professor. When a student learns from a professor, he gets his mark.

My problem is showing list of professors who teach at least 2 students, and 2 students who get best marks from those professors. In example, the query result of this table is:

ProfessorID    StudentID    Mark P1             S1              9 P1             S3             10 P2             S1              7 P2             S3              4 

I’ve tried some solutions but they don’t work right.

How can I do this correctly?

Answer 1

declare  @table table (ProfessorID nvarchar(2), StudentID nvarchar(2),Mark int)  insert into @table select 'P1', 'S1', 9 union all select 'P1', 'S2', 8 union all select 'P1', 'S3', 10 union all select 'P2', 'S1', 7 union all select 'P2', 'S2', 2 union all select 'P2', 'S3', 4 union all select 'P3', 'S4', 5 union all select 'P4', 'S1', 6  select * from @table o where o.StudentID IN (select top 2 s.StudentID from @table s where s.ProfessorId = o.ProfessorId order by Mark DESC) and o.ProfessorID IN (select p.ProfessorID from @table p group by p.ProfessorID having count(*) >= 2)