My SQL skills are very rusty, so need a little assistance.

The record owner on each CRM table allows me to choose the name or the ID of the owner.  Irritatingly, I have a separate user lookup field on a module that only gives me the user ID, but I need the full name.  I've created a concat on the user table called Full Name.  I know I need to do some kind of inner join to reference it, but can't think of how to do it. Any tips?