Re: Documentation of return values of range functions lower and upper

From: Laurenz Albe <laurenz(dot)albe(at)cybertec(dot)at>
To: Fujii Masao <masao(dot)fujii(at)oss(dot)nttdata(dot)com>, jani(dot)rahkola(at)iki(dot)fi, pgsql-docs(at)lists(dot)postgresql(dot)org
Subject: Re: Documentation of return values of range functions lower and upper
Date: 2020-11-18 16:28:44
Message-ID: 02f3fa3a592fa6c1f8ec1a9f539ae376f744eb42.camel@cybertec.at
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On Wed, 2020-11-18 at 22:49 +0900, Fujii Masao wrote:
> On 2020/11/12 17:14, Laurenz Albe wrote:
>
> > On Wed, 2020-11-11 at 18:19 +0100, Laurenz Albe wrote:
> > > > Table 9.54 in page
> > > > https://www.postgresql.org/docs/current/functions-range.html states that the
> > > > functions lower and upper return NULL if the requested bound is infinite. If
> > > > the element type of the range contains the special values infinity and
> > > > -infinity, this is not correct, as those values are returned if explicitly
> > > > used as either bound.
> > > +1
> > > Perhaps it would be better to say
> > > NULL if the range is empty or has no lower/upper bound
>
> I agree this description looks a bit confusing. But according to the section
> "Infinite (Unbounded) Ranges" (*1), we already call "lower/upper bound
> omitted" just infinite. So I don't think the current description is incorrect.
>
> (*1)
> https://www.postgresql.org/docs/devel/rangetypes.html#RANGETYPES-INFINITE

That is correct, but I'd argue that it would be better to clarify the paragraph too,
in particular:

The functions lower_inf and upper_inf test for infinite lower and upper bounds of a range, respectively.

should better read

The functions lower_inf and upper_inf test for omitted lower and upper bounds of a range, respectively.

The rest of the paragraph is pretty unambiguous.

Independent of this, I think that my patch for "upper" and "lower" would make the
documentation clearer.

Yours,
Laurenz Albe

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