public inbox for [email protected]
help / color / mirror / Atom feedFrom: Paul Jungwirth <[email protected]>
To: jian he <[email protected]>
Cc: Peter Eisentraut <[email protected]>
Cc: PostgreSQL Hackers <[email protected]>
Subject: Re: SQL:2011 application time
Date: Mon, 8 Jan 2024 10:54:13 -0800
Message-ID: <[email protected]> (raw)
In-Reply-To: <CACJufxEJAKEVc-Uv6X57BS7=c_wAuPF7RXo7qLdEZWet88r08Q@mail.gmail.com>
References: <CA+renyUApHgSZF9-nd-a0+OPGharLQLO=mDHcY4_qQ0+noCUVg@mail.gmail.com>
<CACJufxGt4oYfa7UN2eAXymgOKH1irbhC5eY_oNkkdj30w-fefw@mail.gmail.com>
<CACJufxExyO_mN8-OkgaTdgqmE5OfE=RBoQXizf=8uRj4c-pAYw@mail.gmail.com>
<CACJufxGeUsmxOhnd2760kBv-hUWRwCy7A0s45pGSPTe8DJVTGw@mail.gmail.com>
<[email protected]>
<[email protected]>
<[email protected]>
<[email protected]>
<[email protected]>
<[email protected]>
<[email protected]>
<[email protected]>
<[email protected]>
<CACJufxG4DvrXD1=Ex2gt2_7U+nF0PZ35qDmqprtFkFd+3E9dTw@mail.gmail.com>
<CACJufxEJAKEVc-Uv6X57BS7=c_wAuPF7RXo7qLdEZWet88r08Q@mail.gmail.com>
On 1/8/24 06:54, jian he wrote:
> On Fri, Jan 5, 2024 at 1:06 PM jian he <[email protected]> wrote:
>
> range_intersect returns the intersection of two ranges.
> I think here we are doing the opposite.
> names the main SQL function "range_not_intersect" and the internal
> function as "range_not_intersect_internal" should be fine.
> so people don't need to understand the meaning of "portion".
Thank you for helping me figure out a name here! I realize that can be a bike-sheddy kind of
discussion, so let me share some of my principles.
Range and multirange are highly mathematically "pure", and that's something I value in them. It
makes them more general-purpose, less encumbered by edge cases, easier to combine, and easier to
reason about. Preserving that close connection to math is a big goal.
What I've called `without_portion` is (like) a closed form of minus (hence `@-` for the operator).
Minus isn't closed under everything (e.g. ranges), so `without_portion` adds arrays---much as to
close subtraction we add negative numbers and to close division we add rationals). We get the same
effect from multiranges, but that only buys us range support. It would be awesome to support
arbitrary types: ranges, multiranges, mdranges, boxes, polygons, inets, etc., so I think an array is
the way to go here. And then each array element is a "leftover". What do we call a closed form of
minus that returns arrays?
Using "not" suggests a function that returns true/false, but `@-` returns an array of things. So
instead of "not" let's consider "complement". I think that's what you're expressing re intersection.
But `@-` is not the same as the complement of intersection. For one thing, `@-` is not commutative.
`old_range @- target_portion` is not the same as `target_portion @- old_range`. But
`complement(old_range * target_portion)` *is* the same as `complement(target_portion * old_range)`.
Or from another angle: it's true that `old_range @- target_portion = old_range @- (old_range *
target_portion)`, but the intersection isn't "doing" anything here. It's true that intersection and
minus both "reduce" what you put in, but minus is more accurate.
So I think we want a name that captures that idea of "minus". Both "not" and "intersection" are
misleading IMO.
Of course "minus" is already taken (and you wouldn't expect it to return arrays anyway), which is
why I'm thinking about names like "without" or "except". Or maybe "multi-minus". I still think
"without portion" is the closest to capturing everything above (and avoids ambiguity with other SQL
operations). And the "portion" ties the operator to `FOR PORTION OF`, which is its purpose. But I
wouldn't be surprised if there were something better.
Yours,
--
Paul ~{:-)
[email protected]
view thread (66+ messages) latest in thread
reply
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Reply to all the recipients using the --to and --cc options:
reply via email
To: [email protected]
Cc: [email protected], [email protected], [email protected], [email protected]
Subject: Re: SQL:2011 application time
In-Reply-To: <[email protected]>
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
This inbox is served by agora; see mirroring instructions
for how to clone and mirror all data and code used for this inbox