[otrs] customer backend unique customer_d

Hi, i think im missing a minor thing but can't find solution. I have a postgresql 8.1.23 DB and otrs 3.1.6. The customer db is currently blank, when i go to add a customer to it via otrs gui i would like the customer_id to be an auto-number but i dont see how to do that. likely some DB magic but im not a dba and little experience in postgres. I can currently add any number to that field. to be clear, what i would like: i enter customer A and he gets customer id number 00001, i enter customer B and he gets number 00002 and so on. Auto number that can't be tampered with from gui, only directly in DB. thank you for any insight. Neil