code: function order($columns){
          $this->rows = null;
          if($columns != ""){
              foreach(func_get_args() as $columns){
                  if($this->union){
                      $this->unionOrder[] = $columns;
                  }else{
                      $this->order[] = $columns;
                  }
              }
          }elseif($this->union){
              $this->unionOrder = array();
          }else{
              $this->order = array();
          }
          return $this;
      }
docs: Add order clause, more calls appends to the end
  
  @param string $columns for example "column1, column2 DESC", empty string to reset previous order
  @param string ...
  
  @return NotORM_Result fluent interface