mysql schema

Hello Am a student trying to learn more about RADIUS server, specifically freeradius. Have a home lab setup were am busy experimenting with freeradius.  My question is, can one create their own mysql schema for freeradius, or it can only work with the provided schema? How do you configure freeradius to use different tables for accounting especially. One other question is, how can freeradius  insert a foreign key into a table. Am asking this because i would like to add a field to the accounting table which is linked to another primary key.  regards bwex