Re: 'infinity'::Interval should be added

On Mon, 17 Dec 2018 at 18:00, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:

> > so I was thinking that
> > postgres=# select 'infinity'::timestamp - 'infinity'::timestamp;
> > would be zero rather than an error, for least surprise.
>
> Wrong. This case needs to be undefined, because "infinity"
> isn't a specific value. That's what makes it okay to define, say,
> infinity plus any finite value as infinity. There are very
> well-defined rules about how to calculate with infinity, and
> not following them is not the way to proceed here.
>
> tl;dr: we should model it after the behavior of IEEE float infinities,
> except we'll want to throw errors where those produce NaNs.
>

Would it be OK to return NULL for ∞ - ∞? Then anybody who wanted 0 could
get it with coalesce (although I think this is a worse idea than anybody
who wants it probably realizes), and anybody who wanted the calculation to
continue on would just get a NULL propagating.

Also am I right to assume that -infinity would use -INT_MAX, etc.? Or
possibly -INT_MAX - 1?