how to limiting user bandwidth by quota..

dear all..i'am using freeradius 1.1.7 on ubuntu 8.04, i do implementing sqlcounter like noresetcounter,dailycounter and montly counter and it works properly. but i now i have 1 case how to limiting user bandwidth usage with sqlcounter, i've read and learn how do sqlcounter work, but i still dont have idea how to make a query to limiting user bandwidth.  i have 1 user and i want to limit the bandwidth for this user 300mb in a week..how to perform this..clue please..really apreciate for your help