• Andy DBA (11/12/2013)The second criteria in the code snippet above won't filter anything, because ALL COLUMNS returned from CourseCompleted will be NULL

    Right you are. In my haste to explain how I learned the lesson to not add a RIGHT table to the WHERE clause of a LEFT join query (it effectively makes it an INNER join), I added to your example and caused your confusion. What I was going for was to expand on your example by adding ISNULL so that it wouldn't produce an empty result set. I just didn't take into account that it wasn't actually doing anything.

    Sorry for my public DUH moment. 😛