Re: range_agg

On Tue, Aug 20, 2019 at 10:33 PM Jeff Davis <pgsql(at)j-davis(dot)com> wrote:
> > Is there any historical discussion around
> > typemods on range types?
>
> I did find a few references:

Thanks for looking those up! It's very interesting to see some of the
original discussion around range types.

Btw this is true of so much, isn't it?:

> It's more a property of the
> column than the type.

Sometimes I think about having a maybe<T> type instead of null/not
null. SQL nulls are already very "monadic" I think but nullability
doesn't travel. I feel like someone ought to write a paper about that,
but I don't know of any. This is tantalizingly close (and a fun read)
but really about something else:
https://www.researchgate.net/publication/266657590_Incomplete_data_what_went_wrong_and_how_to_fix_it
Since you're getting into Rust maybe you can update the wiki page
mentioned in those threads about refactoring the type system. :-)
Anyway sorry for the digression. . . .

> So, I wouldn't spend a lot of time on typmod for multiranges.

Okay, thanks! There is plenty else to do. I think I'm already
supporting it as much as range types do.

Btw I have working multirange_{send,recv,in,out} now, and I
automatically create a multirange type and its array type when someone
creates a new range type. I have a decent start on passing tests and
no compiler warnings. I also have a start on anymultirange and
anyrangearray. (I think I need the latter to support a range-like
constructor function, so you can say `int4multirange(int4range(1,4),
int4range(8,10))`.) I want to get the any* types done and improve the
test coverage, and then I'll probably be ready to share a patch.

Here are a couple other questions:

- Does anyone have advice for the typanalyze function? I feel pretty
out of my depth there (although I haven't looked into typanalyze stuff
very deeply yet). I can probably get some inspiration from
range_typanalyze and array_typanalyze, but those are both quite
detailed (their statistics functions that is).

- What should a multirange do if you give it an empty range? I'm
thinking it should just ignore it, but then `'{}'::int4multirange =
'{empty}'::int4multirange`. Does that seem okay? (It does to me
actually, if we think of `empty` as the additive identity. Similarly
mr + empty = mr.

- What should a multirange do if you give it a null, like
`int4multirange(int4range(1,4), null)`. I'm thinking it should be
null, just like mr + null = null. Right?

Thanks!
Paul