Re: empty range

From: david(dot)turon(at)linuxbox(dot)cz
To: "Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: emre(at)hasegeli(dot)com, pgsql-hackers(at)postgresql(dot)org
Subject: Re: empty range
Date: 2020-01-20 07:39:35
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> regression=# select int4range(4,4) = int4range(5,5);
> ?column?
> ----------
> t
> (1 row)

Yes you have right, i don't realize this situation. But what about yust
leave empty bit set to True and don't discard the input value - items can
be sort and we can see the value - lower(int4range(4,4)) can be 4 without
any damage. There is isempty function and i hope nobody check empty ranges
with lower(anyrange) IS NULL AND upper(anyrange) IS NULL right?

Another thing that we did not know before was that is better store
tstzrange(now(), NULL) instead of tstzrange(now,'infinity') becouse
upper_inf is not True in this case and is not True if bounds are closed
'[]'. Maybe we did not read documentation properly and we did not know how
is range type stored internally and we was confused after discovering this

SELECT upper_inf(tstzrange(now(),'infinity','[]'));
(1 řádka)

Best regards

David T.

Ing. David TUROŇ, s.r.o.
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Od: "Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Komu: emre(at)hasegeli(dot)com
Kopie: david(dot)turon(at)linuxbox(dot)cz, pgsql-hackers(at)postgresql(dot)org
Datum: 16. 01. 2020 16:21
Předmět: Re: empty range

Emre Hasegeli <emre(at)hasegeli(dot)com> writes:
>> It's only suggestion, i don't now if somebody wants store empty range
without bounds.

> I thought about the same while developing the BRIN inclusion operator
> class. I am not sure how useful empty ranges are in practice, but
> keeping their bound would only bring more flexibility, and eliminate
> special cases on most of the range operators. For reference, we allow
> empty boxes, and none of the geometric operators has to handle them
> specially.

I think it'd just move the special cases somewhere else. Consider

regression=# select int4range(4,4) = int4range(5,5);
(1 row)

How do you preserve that behavior ... or if you don't, how much
damage does that do to the semantics of ranges? Right now there's
a pretty solid set-theoretic basis for understanding what a range is,
ie two ranges are the same if they include the same sets of elements.
It seems like that goes out the window if we don't consider that
all empty ranges are the same.

BTW, I think the main reason for all the bound-normalization pushups
is to try to have a rule that ranges that are set-theoretically equal
will look the same. That also goes out the window if we make
empty ranges look like this.

regards, tom lane

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