try that one:
PHP Code:
$users = $DB_site->query("
SELECT DISTINCT
$classfieldselect userclass.title, user.userid, user.username, user.userclassid, user.userclassid,
user.usergroupid
FROM user
LEFT JOIN userclass ON (userclass.userclassid = user.userclassid)
LEFT JOIN userfield ON (userfield.userid = user.userid)
LEFT JOIN usergroup ON (usergroup.usergroupid = user.usergroupid)
WHERE usergroup.rollcall = 1
");