Retroactive billing report in oracle order management

SELECT DECODE (:p_sort_by, 'O', orig_head.order_number) sort_by_order_number,

       DECODE (

          :p_sort_by,

          'T', oe_retrobill_pvt.invoice_number (orig_head.order_number,

                                                orig_lin.line_id,

                                                orig_head.order_type_id),

          NULL)

          sort_by_invoice_no,

       DECODE (

          SUBSTR (UPPER (:p_item_display), 1, 1),