$sql2 = "SELECT c1.ID, c1.si, c2.si, c2.ID as parent_id
              FROM v_menu c1
              LEFT JOIN v_menu c2
              on (c2.parent = c1.ID)
              WHERE (c1.ID = :c1)";
      $st2 = $this->db->prepare($sql2);
      $st2->execute(array(':c1' => $row['MID'])); // $row['MID'] => product category
      $res2 = $st2->fetchAll();