Re: inconsistent composite type null handling in plpgsql out variable

On Mon, Aug 31, 2009 at 07:26:59PM +0200, Pavel Stehule wrote:
> 2009/8/31 Sam Mason <sam@samason.me.uk>:
> > The more awkward case (to me anyway) is that the standard says (1,NULL)
> > IS NULL should evaluate to TRUE.
>
> what?
>
> only (NULL, NULL) IS NULL is true

Bah, sorry you're right!  I was rattling my favorite tin and getting
mixed up with the behavior with IS NOT NULL, the negation of which
would say this row is null.  I.e:

  SELECT NOT (1,NULL) IS NOT NULL;

evaluates to TRUE.  I think the consensus is that we should continue to
follow the spec on this, but I was getting confused as to which operator
contains the EXISTS and FORALL operator.  I.e. a value "v" IS NULL iff
all elements of "v" are not 'the null value', whereas "v" IS NOT NULL
iff an element of "v" is 'the null value'.

> p.s. what isn't consistent (maybe - there are more possible
> interpretations) is
>
> (NULL, NULL) IS DISTINCT FROM NULL is true

Yup, I'd agree with Merlin that a ROW consisting entirely of 'null
values' should itself be 'the null value' (to use the terminology from
the copy of the SQL spec I'm reading).  I think this should also work
recursively:

  SELECT ROW(ROW(NULL)) IS DISTINCT FROM NULL;

should return FALSE, in my understanding.

--
  Sam  http://samason.me.uk/