class HighWaterTest

class HighWaterTest extends SqlBase {
  
  /**
   * {@inheritdoc}
   */
  public function query() {
    $field_names = array_keys($this->fields());
    $query = $this->select('high_water_node', 'm')
      ->fields('m', $field_names);
    foreach ($field_names as $field_name) {
      $query->groupBy($field_name);
    }
    return $query;
  }
  
  /**
   * {@inheritdoc}
   */
  public function fields() {
    $fields = [
      'id' => $this->t('Id'),
      'title' => $this->t('Title'),
      'changed' => $this->t('Changed'),
    ];
    return $fields;
  }
  
  /**
   * {@inheritdoc}
   */
  public function getIds() {
    return [
      'id' => [
        'type' => 'integer',
      ],
    ];
  }

}