I’ll se if I can explain this properly. I’m not that good at explanations.
I have a database table with titles and studios as two columns. It’s a list of cartoons and the studios they were developed at. The studios column (an integer value) is linked to a studios table. So we can get that with a join:
JOIN iad_titles on iad_studios.id = iad_titles.studio
But we also have a link table for associated studios with the fields titleNo and studioNo.
Now … ALL the cartoons are going to have a main studio listing. They may not have a listing in the associated studios But when I search for cartoons by the studio, I want to find all the toons that connect to that studio as well as all the ones that might have an associated studio listed.