IF NEW.some_field IS DISTINCT FROM OLD.some_field THEN
IS DISTINCT FROM is like <> except that it treats NULL as an ordinary
value.
thanks - i didn't know about this operator.
> CREATE TRIGGER impossible_to_change BEFORE UPDATE ON some_table FOR EACH ROW
> EXECUTE PROCEDURE impossible_to_change();
If the table has other triggers and you don't want them to modify
the value either, then the check should probably go in an AFTER
trigger.
i would rather use before anyway.
the problem with after is that in aftrer - all you can do is to raise exception. while - if you would like to value to stick - you would ahve to change the code *and* change trigger declaration. putting it in before solves the problem.
of course there might be problem with another triggers, but that's another story.
depesz
