I have this person table as super parent, id firstname lastname email telephone ... ... and user table as a child id person_id (FK) password username screenname ... ... They must be 1:1 ...
Let me give you a little setup. We have a InnoDB table on MySQL 5.1 with close to 20 million records, no foreign keys, and proper indexes for queries we do. We are using the latest 6.3.5 MySQL ...