[otrs] Database question

Hello, I'm afraid there will be more of these questions coming.. In table ticket it seems there is no link to the user table, there is only customer_user and customer_user_id. Both of the field are varchar's and don't link to user.id. That surprised me, what happens if I rename the account. Are the tickets that where created under the old name lo longer linked, or are they updated by otrs if I rename the account? Why not link to the user.id? Bas