Re: range_adjacent and discrete ranges

Jeff Davis <pgsql@j-davis.com> writes:
> On Fri, 2011-11-18 at 14:47 -0500, Tom Lane wrote:
>> Yeah, probably not.  However, I don't like the idea of
>> '(3,4)'::int4range throwing an error, as it currently does, because it
>> seems to require the application to have quite a lot of knowledge of the
>> range semantics to avoid having errors sprung on it.

> OK, then let's make '(3,4)'::int4range the empty range. (3,3) might be
> OK as well (for any range type), because at least it's consistent.

> The one that I find strange is [3,3), but I think that needs to work for
> the range_adjacent idea to work. Seeing it as useful in the context of
> range_adjacent might mean that it's useful elsewhere, too, so now I'm
> leaning toward supporting [3,3) as an empty range.

OK, so the thought is that the only actual error condition would be
lower bound value > upper bound value?  Otherwise, if the range
specification represents an empty set, that's fine, we just normalize it
to 'empty'.  Seems consistent to me.
        regards, tom lane