SQL & PL/SQL

I have a table which has bookings made by users and in the insert_user field we put in their UID's, so we know which user has made which booking.

Now I have to insert all these records in another database. I'll create the same type of table but what to do about the uid for the users. If I insert the same uid in this database, it will have no meaning as that uid might be assigned to someone else in this database or it might not even be existing. What to do in this case? Do I need to create the same user again in this database, but then he wont have the same uid as the other database. Can I do something where one user will have the same UID in both the databases? Please advise. Thanks.