$onlineNow = $DB_site->query( "SELECT s.userid, u.username, s.location FROM session s, users u WHERE u.userid = s.userid AND u.invisible = 0 ORDER BY u.username ASC" );

$onlineNow = $DB_site->query( "
SELECT s.userid,
u.username,
s.location
FROM session s
LEFT OUTER JOIN user u 
  ON u.userid = s.userid
WHERE u.invisible = 0 OR 
      u.invisible IS NULL
ORDER BY u.username ASC" );

    $username = $online[ username ];

    if( $online[ username ] != "" ) {
      $username = $online[ username ];
    } else {
      $username = "Guest";
    } // end if