code: public function getPageHistoricListOfActions($order = 'ASC')
      {
          $select = $this->tableGateway->getSql()->select();
          $select->columns(["action" => new Expression('DISTINCT(hist_action)')]);
          $select->order('hist_action' . ' '  . $order);
          $resultSet = $this->tableGateway->selectWith($select);
  
          return $resultSet;
      }
docs: This will return all distinct actions
  @param string $order
  @return mixed