Blaise Carrupt wrote:
> Hi all !
>
> I use PostgreSQL 7.0.2 on a HP-UX system.
>
> I would like to create a simple function and a simple trigger (or rule) that
> deny a delete from a table if the row is referenced in another table.
>
> I though it should look like this (from my Ingres experience... :) :
>
> create function A_del(int4 i_id)
> BEGIN
> SELECT id
> FROM b
> where a_id = :i_id;
>
> if rowcount > 0 then
> RAISE EXCEPTION "not allowed !"
> end if;
> END
>
CREATE FUNCTION A_del () RETURNS opaque AS ' DECLARE nrefs integer; BEGIN nrefs
:=count(*) FROM b WHERE a_id = OLD.i_id; IF nrefs > 0 THEN RAISE EXCEPTION ''a_id % still
referencedfrom b'', OLD.i_id; END IF; RETURN OLD; END;' LANGUAGE 'plpgsql';
>
> create trigger before delete from A for each row execute procedure A_del(old.id)
CREATE TRIGGER A_del BEFORE DELETE ON A FOR EACH ROW EXECUTE PROCEDURE A_del();
>
>
> But it seems to be much more complicated with Postgres (create a C function
> using CurrentTriggerData,...). May I have missed something or is it really much
> more complicated ?
Alternatively (IMHO preferred) you could use a referential integrity constraint in table B, which would
also cover UPDATE on A and check values inserted/updated into/in B.
CREATE TABLE B ( ... FOREIGN KEY (i_id) REFERENCES A (a_id)
Jan
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