Question

I’m in desperate need of some help here.

My problem is this: There are two tables in my database, tblSubmission and tblStudent. tblStudent is linked with tblSubmission by the student_id key. Some of the rows in tblStudent have been deleted, and are therefore unlinked to their row in tblSubmission.

What I need to do is compare the two tables, and find the student_id‘s that exist in tblSubmission, but NOT in tblStudent, but the results from tblSubmission have to have a column where app_id equals 358.

Checking through these rows manually is not an option since there are thousands of them. I’ve tried many queries already, using the most SQL I know and clauses like NOT EXISTS and NOT IN, but to no avail.

Answer 1

This will show all records in tblSubmission that have not a correlated record in tblStudent:

SELECT tblSubmission.*
FROM tblSubmission left join tblStudent on tblSubmission.student_id = tblStudent.student_id
WHERE tblStudent.student_id is null
      AND app_id = 358

or also:

SELECT tblSubmission.*
FROM tblSubmission
WHERE student_id not in (select student_id from tblStudent)
      AND app_id = 358