>select * from table1;
>where keyfield IN;
>(select keyfield from MyNotInTable)
>
>Again, the tables relations, ability to determine records' in/not in status, maintainance nightmares, etc. might be prohibitive, but just a thought to provoke your thoughts.

Unfortunately, this has to be done freshly each time. However, it's an admin-only task, and only needs to be run every few weeks on a bunch of tables. Once I get it operational, an admin can just start it up and do something else for an hour or so...