Re: Odd system-column handling in postgres_fdw join pushdown patch

Robert Haas <robertmhaas@gmail.com> writes:
> On Wed, Apr 13, 2016 at 1:36 PM, Robert Haas <robertmhaas@gmail.com> wrote:
>> I tend to favor zeroes rather than NULLs, because that's what we
>> typically use to represent an invalid value of those types, and I'm
>> not aware of any current case where those values are NULL.

> In fact, see heap_attisnull.

Right, a table's system columns cannot be null at the table-scan level.
(But they could go to null above an outer join.)
        regards, tom lane