Issue #1923816 by alexpott, quietone, ayushmishra206, jhodgdon, chx, Lendude:...

   *       ->aggregate('nid', 'count')

   *       ->condition('status', 1)

   *       ->groupby('type')

   *   ->executeAggregate();

   *       ->execute();

   *   @endcode

   *   Will return:

   *   @code

   *     $result[0] = array('count_nid' => 3, 'type' => 'page');

   * $result[1] = array('count_nid' => 1, 'type' => 'poll');

   * $result[2] = array('count_nid' => 4, 'type' => 'story');

   *     $result[1] = array('count_nid' => 4, 'type' => 'article');

   *   @endcode

   */

  public function execute();