public function groups(){
    $a =& $this->class_cfg['arch'];
    $t =& $this->class_cfg['tables'];
    $id = $this->db->cfn($a['groups']['id'], $t['groups'], 1);
    $group = $this->db->cfn($a['groups']['group'], $t['groups'], 1);
    $id_group = $this->db->cfn($a['users']['id_group'], $t['users'], 1);
    $active = $this->db->cfn($a['users']['active'], $t['users'], 1);
    $users_id = $this->db->cfn($a['users']['id'], $t['users'], 1);
    $groups = $this->db->escape($t['groups']);
    $users = $this->db->escape($t['users']);
    return $this->db->get_rows("
      SELECT $id, $group,
      COUNT($users_id) AS `num`
      FROM $groups
        LEFT JOIN $users
          ON $id_group = $id
      GROUP BY $id");
  }