trigger problem

I am writting a trigger, I have table parts(PNO,..,QOH,..), before delete the PNO row, I need to check QOH. Part of the trigger code like:
create or replace trigger parts_bef_del_row before delete on parts
for each row

declare
  num integer := 0;

  cursor plc is
  select *
  from parts
  where pno = :old.pno;

When I tried the trigger, it gave me:
LINE/COL ERROR

-------- -----------------------------------------------------------------
7/19     PLS-00049: bad bind variable 'OLD.PNO'

In fact my old.pno is not on line 7 at all, what is wrong, please help and thanks. Received on Sun Nov 23 2003 - 17:21:32 CET