Re: Document "59.2. Built-in Operator Classes" have a clerical error?

On Sun, Aug 2, 2020 at 08:43:53PM -0700, David G. Johnston wrote:
> On Sun, Aug 2, 2020 at 8:17 PM osdba <mailtch(at)163(dot)com> wrote:
>
> hi all:
>
> In Document "Table 59-1. Built-in GiST Operator Classes":
>
> "range_ops any range type && &> &< >> << <@ -|- = @> @>"， exist double "@>
> "，
>  
> Should be "<@ @>" ?
>
>
>
> It helps to reference the current version of the page (or provide a url link)
> as that section seems to have migrated to Chapter 64 - though it is unchanged
> even on the main development branch.
>
> The table itself is extremely difficult to read: it would be more easily
> readable if the font was monospaced, but its not.
>
> I'm reasonably confident that the equal sign is part of the second-to-last
> operator while the lone @> is the final operator.  Mostly I say this because
> GiST doesn't do straight equality so a lone equal operator isn't valid.

I dug into this. This query I think explains why the duplicate is
there:

SELECT oprname, oprleft::regtype, oprright::regtype, oprresult::regtype
FROM pg_am
JOIN pg_opclass ON opcmethod = pg_am.oid
JOIN pg_amop ON opcfamily = pg_amop.amopfamily
JOIN pg_operator ON amopopr = pg_operator.oid
WHERE amname = 'gist'
AND opcname = 'range_ops'
ORDER BY 1

oprname | oprleft | oprright | oprresult
---------+----------+------------+-----------
&& | anyrange | anyrange | boolean
&< | anyrange | anyrange | boolean
&> | anyrange | anyrange | boolean
-|- | anyrange | anyrange | boolean
<< | anyrange | anyrange | boolean
<@ | anyrange | anyrange | boolean
= | anyrange | anyrange | boolean
>> | anyrange | anyrange | boolean
--> @> | anyrange | anyrange | boolean
--> @> | anyrange | anyelement | boolean

Notice that @> appears twice. (I am not sure why @> appears twice in
the SQL output, while <@ appears only once.) The PG docs explain the
duplicate:

https://www.postgresql.org/docs/12/functions-range.html

@> contains range int4range(2,4) @> int4range(2,3) t
@> contains element '[2011-01-01,2011-03-01)'::tsrange @> '2011-01-10'::timestamp t
<@ range is contained by int4range(2,4) <@ int4range(1,7) t
<@ element is contained by 42 <@ int4range(1,7) f

There is an anyrange/anyrange version, and an anyrange/anyelement
version of @> and <@. Anyway, for the docs, I think we can either
remove the duplicate entry, or modify it to clarify one is for
anyrange/anyrange and another is for anyrange/anyelement. I suggest the
first option.

--
Bruce Momjian <bruce(at)momjian(dot)us> https://momjian.us
EnterpriseDB https://enterprisedb.com

The usefulness of a cup is in its emptiness, Bruce Lee