Question

 TABLE A
 id=1
+file_id=100
|
| TABLE B
|id=1
+file_id=100
|
|TABLE FILES
>id=100
 file_name = picture.jpg
 file_size = 99999

file_id of TABLE A and TABLE B are in connection width TABLE FILES id.

I would like to check if any of the two table records are pointed to the file with let sey id=100. If not the file would be deleted.

How can I do this?

Answer 1

Delete the results of the query:

SELECT filename 
FROM files f
WHERE (
     NOT EXISTS (SELECT * FROM A WHERE file_id= f.id) 
     AND NOT EXISTS (SELECT * FROM B WHERE file_id = f.id)
)

This (ideally) gets the files which are not referenced in either A or B