How to Find the PO Number If We Give the Requisition Number?

SELECT POH. PO_HEADER_ID, POH. SEGMENT1 PO_NO , PRHA .SEGMENT1 REQUISTION_NO
FROM APPS.PO_HEADERS_ALL POH, 
     APPS.PO_DISTRIBUTIONS_ALL PDA ,
     APPS.PO_REQ_DISTRIBUTIONS_ALL PRDA ,
     APPS.PO_REQUISITION_LINES_ALL PRLA ,
     APPS.PO_REQUISITION_HEADERS_ALL PRHA
WHERE POH. PO_HEADER_ID = PDA. PO_HEADER_ID 
AND   PDA. REQ_DISTRIBUTION_ID = PRDA.DISTRIBUTION_ID
AND   PRDA. REQUISITION_LINE_ID = PRLA. REQUISITION_LINE_ID
AND   PRLA. REQUISITION_HEADER_ID = PRHA. REQUISITION_HEADER_ID
--AND   POH.SEGMENT1 = &1   -- PO NUMBER 
AND    PRHA. SEGMENT1 =&2   -- PO REQUISITION NUMBER