For the tables user_teachers and user_students, there are both userid and id.  From my understanding, userid is the actual id of the user (id field in user table) and id (in the user_teachers and user_students) table is implemented so that a single user can be bound to more than one course number.  If my assumption is correct, than the auto increment of id (in the user_students and user_teachers) table should increment the max number found in the id field of the respective tables and not the maximum number found in the id field of the user table.  I am asking this question because I wish to use our own userids from other databases and set them into the user table and then bind these users to certain courses.  Could I just auto increment the max number found in th id field of the user_teachers and user_students table starting from 0 even though I have random user id numbers?  Thanks for the help.