Influence of deferred constraint to Table is mutating proble

Question

Hello,
i have a question regarding the 'Table is mutating,
Trigger/Function may not see it'-problem. I
wondered whether a deferrable constraint can solve the problem,
but as I tested it, it's the same
behaviour as before.
Situation:
assume tables LOC_TO and TORDER and the following constraint:
ALTER TABLE LOC_TO ADD (CONSTRAINT LT_TOID FOREIGN KEY (LT_TOID)
REFERENCES TORDER ON DELETE CASCADE
DEFERRABLE INITIALLY DEFERRED);
assume a trigger on table TORDER:
create or replace trigger tIU_TORDER_ADD
after insert or update of TO_STATE on TORDER
for each row
declare
begin
insert
into loc_to
( lt_locid,
lt_toid )
values
( 'HRL14042',
:new.to_id )
end tIU_TORDER_ADD;
I thought, that on a deferred constraint at the triggered action
no check to TORDER is done, and
that this fact will prevent the ORACLE_ERROR ORA-04091.
Can anyone tell me, why this doesn't work?
Thanks
Titus Leskien
null

Answer 1

There was a loophole in the mutating table gotcha: single row inserts in a BEFORE EACH ROW trigger were not considered mutating, but were in AFTER EACH ROW triggers. This did not apply to INSERT INTO ... SELECT ... statements, which always mutated, even if they only inserted one row.
This is get-out is no longer included in the documentation, but as you have found still applies in the 9.2 database (and it's unlikely Oracle will have broken it in 10g).
Cheers, APC