Re: freezing a particular field in a table

On 11/23/05, Michael Fuhr <mike(at)fuhr(dot)org> wrote:
>
> 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