code: public OrderItem createOrderItem() {
          if (orderByItemSegment instanceof IndexOrderByItemSegment) {
              return createOrderItem((IndexOrderByItemSegment) orderByItemSegment);
          }
          if (orderByItemSegment instanceof ColumnOrderByItemSegment) {
              return createOrderItem(selectStatement, (ColumnOrderByItemSegment) orderByItemSegment);
          }
          if (orderByItemSegment instanceof ExpressionOrderByItemSegment) {
              return createOrderItem(selectStatement, (ExpressionOrderByItemSegment) orderByItemSegment);
          }
          throw new UnsupportedOperationException();
      }
docs: Create order item.
  
  @return order item