Question

Let’s say I have the following tables

Collection DirectorId StudioId
   1             NULL      1
   2             2         NULL
   3             NULL      2


Director MovieId
  1        1
  2        4

Studio   MovieId
  1        1
  2        3
  2        4
  1        2

The collection table will always have either director or studio id but never both.

How could I write a query to get all the movies in one a collection so that I end up with

CollectionID MovieID
1            1
1            2
2            4
3            3
3            4

I hope this makes sense

Answer 1

This should work (not sure about your column names, but you get the idea):

select c.CollectionID, isnull(d.MovieId, s.MovieId) MovieID
from Collection c
left join Director d on d.Director=c.DirectorId
left join Studio s on s.Studio=c.StudioId