Purchase Requisition Status Report query--- Need Help

Hi,

I have the query for Purchase Requisition Status Report.In this query problem is: If suppose PO is cancelled , Order_Number & PO_STATUS cloumn coming  blank.

/* Formatted on 2013/02/04 14:28 (Formatter Plus v4.8.8) */
SELECT prh.segment1 requistion_number,
       TO_CHAR (prh.creation_date,
                'DD-MON-RRRR   HH24:MI:SS'
               ) req_creation_date,
       prl.line_num line_number,
       prh.authorization_status po_requistion_status,
       aps.vendor_name vendor_name,
       TO_CHAR (ph.creation_date, 'DD-MON-RRRR   HH24:MI:SS') creation_date,
       pl.line_num, prl.item_description item_description,
       prl.quantity quantity, prl.unit_meas_lookup_code unit_meas_lookup_code,
       prl.unit_price unit_price,