title: Primary Key as domain username AND userID?
body: <p>I have read here that it is probably better to use an AI integer to denote users as opposed to an assigned domain (string) username.  I can accept that, however, when I am including in the 'users' table the auto generated userid and the unique domain usernames, how should I denote that in other tables as FKs?  eg.  Department table with 'userid' AND 'domainname' or just userid; hardware table with 'userid' AND 'domainname' or just 'userid' as owner?</p>