What is wrong with this:
SELECT student.sid, test_results . *
INNER JOIN test_results ON student.sid = test_results.ID
WHERE student.district_code = 'OSD'
Attached are the structures of both tables.
There are 6899 records in student where district_code = 'OSD'.
My guess is there are about 500K records in test_results that meet these criteria. The query result says returned zero.