So when you have the two tables, what I used to do
is get out a notebook, and I would write down ZATTACHMENT,
Z_PK, ZVIBERMESSAGE, and I would circle the two things
that they had in common.
That way, I knew how I was going to join it.
Where most students have an issue, they will find this.
They'll say, OK, ZATTACHMENT Z_PK
equals ZVIBERMESSAGE ZATTACHMENT,
but then they don't ask for anything,
so your query never changes.
We want to say, when these two things are in common,
show us the file name, or the file path, or the file size--
anything you want at that point.