I have to tables (A and B), and I want to delete records from both of
them that exist in both of them. If a record exists in only one, then
I don't want to delete it.

This would be the easiest way to do it:

delete from A where id in (select id from B)

The problem is that after I delete them table A, I loose my record of
what to delete from B, so I can't follow up with:

delete from B where id in (select id from A)

as the records have already gone.

Any suggestions?

Robert Munro