Accounting data and NULL sessions

I have two questions if I may. One I think I've asked before but just getting around to trying to tackle it again. 1. I am using mysql for radacct data to keep track of sessions. The accounting data is going into flat files on each radius server. Is there a way to get the accounting data to go directly to into a mysql table? I don't want the accounting data in radacct. 2. I have multiple NULL sessions in my radacct file??? What causes these and how do folks deal with them? Thanks, N