I have two tables A, B
A has a field Ptr which can be 0 or can point to an Index of B
I need to know which indices of B are not pointed to by A.
i.e., which ptrs are missing from A.
Again, note that A has extra fields where the ptr is 0 and that's okay.
I could make another field in B (and later erase it) to "tally" if A points to it, and then i have the missing indices, but i'm guessing there's a more elegant way to JOIN or compare to accomplish this.