关于触发器无法更新多行问题

单一品号当状态更新后可更新，多个品号(多行)无法更新，触发器如下：
 create or replace trigger AA_PR_LINES_UPDATE_T1
   after insert or update on "PO"."PO_REQUISITION_HEADERS_ALL"
     referencing new as new
   for each row
 when (new.AUTHORIZATION_STATUS='APPROVED' and
       new.requisition_header_id is not null)
 begin
 declare
   p_header_id number;
   p_line_id   number;
   p_line_num  number;
   ax          number;
   bx          number;
   p_item_id   NUMBER;
 begin
 select prl.item_id,prl.blanket_po_header_id,prl.blanket_po_line_num,prl.requisition_line_id
   into p_item_id,ax,bx,p_line_id
 from po_requisition_lines_all prl
 where prl.requisition_header_id=:new.requisition_header_id;
 select po_header_id,line_num into p_header_id,p_line_num
   from (select ROW_NUMBER() OVER(ORDER BY pol.unit_price) rownumber
               ,poh.po_header_id,pol.line_num,s.vendor_name,ass.vendor_site_code,poh.vendor_id
               ,ass.vendor_site_id,poh.segment1,pol.unit_price,pol.attribute1,pol.attribute2
               ,pol.item_id
           from po_headers_all poh,po_lines_all pol,ap_suppliers s,ap_supplier_sites_all ass
          where poh.po_header_id = pol.po_header_id
            and poh.type_lookup_code = 'BLANKET'
            and pol.item_id =p_item_id
            and poh.approved_flag = 'Y'
            and NVL(pol.closed_code, 'OPEN') = 'OPEN'
            and pol.creation_date || '-' || poh.vendor_id in (select max(pol.creation_date) || '-' || poh.vendor_id
                                                                from po_headers_all poh,
                                                                     po_lines_all   pol
                                                               where poh.po_header_id = pol.po_header_id
                                                                 and poh.type_lookup_code = 'BLANKET'
                                                                 and pol.item_id = p_item_id
                                                                 and NVL(pol.closed_code,'OPEN') = 'OPEN'
                                                                 and nvl(pol.cancel_flag,'N') = 'N'
                                                                 and poh.approved_flag = 'Y'
                                                               group by poh.vendor_id)
            and nvl(pol.cancel_flag, 'N') = 'N'
            and poh.vendor_id=s.vendor_id
            and s.vendor_id=ass.vendor_id)
 where 1 = 1
    and rownumber = 1;
 
   if ax<>p_header_id /*and bx<>p_line_num*/ then
    update PO_REQUISITION_LINES_ALL prl 
      set prl.blanket_po_header_id=p_header_id
          ,prl.blanket_po_line_num=p_line_num
          
    where prl.requisition_header_id=:new.requisition_header_id
      and prl.item_id=p_item_id
      and prl.requisition_line_id=p_line_id;
      commit;
      end if;
 
   exception
     when others then null;
 end;
 end;
 请高手帮忙看下哪里写错了。