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Asked: 2026-05-27T14:16:26+00:00

I’ve been hours trying to build this query and I need your help so

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I’ve been hours trying to build this query and I need your help so I can make it.
This is table Students (made out of inner joins): 

SpecialtyChosenID  StudentID    Subject    SubjectSpecialtyID
5ABFB416-8137         15        Math          A1EBF3CB-E899
5ABFB416-8137         15        English       A1EBF3CB-E899

The info in it means that a student with id no. 15 has chosen an specialty with id 5ABFB416-8137

The two subjects he has passed (Math and English) belong to a specialty with id A1EBF3CB-E899

What would be the query to know if the passed subjects belong to the specialty chosen by the student??

Counting the number of subjects with the same SubjectSpecialtyID as SpecialtyChosenID and vice versa could do.

Thanks a lot

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1 Answer

  1. Editorial Team

    You can do a self join. This finds the number of subjects taken by the student that match the student’s chosen specialities.

    SELECT l.SpecialtyChosenID, l.StudentID, Count(Distinct r.Subject) FROM Students l
LEFT JOIN Students r ON (l.StudentID=r.StudentID AND l.SpecialityChosenID=r.SubjectSpecialityID)
GROUP BY l.SpecialtyChosenID, l.StudentID

    However, this is quite inefficient using the table structure given. If you have a table listing students with their specialities, and another with subjects and specialities, and a third relating students with subjects, it would be better to build this query from the base data, rather than from the derived data.

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