function queryColumn($query)
  {
    $data = [];
    $res = $this->q($query);
    while ($row = $res->fetch_row())
    {
      if ($res->field_count == 1)
        $data[] = $row[0];
      else
        $data[$row[0]] = $row[1];
    }
    $res->close();
    return $data;
  }