Re: Is there a way to test for UNASSIGNED in pl/pgsql

2012/10/29 Tom Lane <tgl@sss.pgh.pa.us>:
> Hannu Krosing <hannu@2ndQuadrant.com> writes:
>> Would just converting UNDEFINED to NULL be a very bad idea ?
>
> Yeah, it would, at least for the normal case where an undefined record
> variable has no well-defined type either.  Saying that it's NULL doesn't
> provide an answer to what type it has.
>
> In the case of OLD/NEW we do know that they ought to have the rowtype of
> the underlying table, so it's conceivable that we could pretend they are
> nulls of that type.  But then you get into the question of whether a
> NULL record is distinguishable from (NULL, NULL, ...) --- which would be
> a perfectly legal real value of these records.  Note that the SQL
> standard is pretty firmly on the side that says they are not
> distinguishable.  I don't agree with that personally, but I don't think
> it'd be a good idea to make a fundamental plpgsql feature depend on
> being able to distinguish these states.
>
> TBH, I think your request is ill-considered and should be rejected.
> There is nothing whatsoever wrong with testing TG_OP to see what sort of
> trigger you're in.

+1

we can define two vars TG_NEW_IS_VALID and TG_OLD_IS_VALID.

and then you can write test

IF TG_NEW_IS_VALID THEN -- do some with NEW
ELSE -- ...
END IF;

Regards

Pavel

>
>                         regards, tom lane