Mine

    /**
     * Count the users in room
     * 
     * @param  string roomId
     * @return int    the count of users
     * 
     * @global Db
     */
    public function countUsersInRoom($roomId) {
        global $Db;
        $Db->execute(
            'SELECT COUNT(*) AS count ' .
            'FROM chatdata, usersinrooms ' .
            'WHERE chatdata.ischatting=1 AND chatdata.uid!=0 AND usersinrooms.room=%s ' .
            'AND usersinrooms.id=chatdata.uid AND usersinrooms.id!=0',
            $roomId
        );
        $tmpCount = $Db->fields[0]['count'];
        $Db->execute('SELECT id FROM chatrooms WHERE p_id=%u', $roomId);
        $fields = $Db->fields;
        for ($i = 0, $max = $Db->recordCount(); $i < $max; $i++) {
            $Db->execute(
                'SELECT COUNT(*) AS count ' .
                'FROM chatdata, usersinrooms ' .
                'WHERE chatdata.ischatting=1 AND usersinrooms.room=%s AND usersinrooms.id=chatdata.uid AND uid!=0',
                $fields[$i]['id']
            );
            $tmpCount += $Db->fields[0]['count'];
        }
        
        return $tmpCount;
    }