Please help!!! about this damn triggers!?

Question

Hi,
I wrote a trigger for a table in my database ,here is the code :
DECLARE
     NO_NUMBER NUMBER(1);
     pret_nou number(10);
     BEGIN
     IF UPDATING THEN
          SELECT COUNT(*) INTO pret_nou FROM OCT_ART_DIF WHERE ART_NO = :NEW.art_no;
          IF NO_NUMBER != 0 THEN
          select sell_pr into pret_nou from article where ART_NO = :NEW.art_no;
               update modif_pr set sell_pr=pret_nou where art_no= :NEW.art_no;
          END IF;
     end if;
end;
I have no compilation error but when it fire , the user who update the OCT_ART_DIF cannot save the data.
Can anyone tell me why ?
Thanks

Answer 1

I'm afraid you misunderstood my reply. I didn't mean you
personally couldn't select from that table, I meant Oracle does
not permit any trigger to do any select or DML on the table to
which the trigger belongs: you can't fire a trigger on SCOTT.EMP
that selects from SCOTT.EMP. It's the law.
The reason is simple: by definition the trigger is firing whilst
the table is in a state of flux - you're changing the table data,
that's why the trigger is firing. This means that a SELECT or
any DML on the triggering data cannot produce predictable or
consistent results.
For instance, what value should a query return :NEW.column_name
or :OLD.column_name?
Or consider your particular case: you're checking for the
existence of other records with a particular value. If you
insert three records with that value, each time the trigger fired
it would logically produce a different result -0, 1, 2. Is that
correct?
The answer to these questions is "It might be, it might not be."
Oracle resolves these tricky problems by saying: you can't do
that. It isn't pretty but at least it is consistent and
predictable.
If you really want to do this, then as someone suggested, you
need to hive it out to a PL/SQL procedure. You can use DBMS_JOB
to fire an updating routine in (say) 1 second's time.
rgds, APC