Re: Range Types: << >> -|- ops vs empty range

From: "Kevin Grittner" <Kevin(dot)Grittner(at)wicourts(dot)gov>
To: "Robert Haas" <robertmhaas(at)gmail(dot)com>, "Jeff Davis" <pgsql(at)j-davis(dot)com>
Cc: <pgsql-hackers(at)postgresql(dot)org>,"Erik Rijkers" <er(at)xs4all(dot)nl>
Subject: Re: Range Types: << >> -|- ops vs empty range
Date: 2011-02-11 17:46:25
Message-ID: 4D552191020000250003A85F@gw.wicourts.gov
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Jeff Davis <pgsql(at)j-davis(dot)com> wrote:

> ">>" means "strictly right of"
> "<<" means "strictly left of"
> "-|-" means "adjacent" (touching but not overlapping)
>
> I'm open to suggestion about how those behave with empty ranges.

OK, that still leaves a lot to the imagination, though. To try to
clarify in *my* mind:

"empty range"
=============
Zero length?
If so, is it fixed at some point, but empty?
'(x,x)'?
'[x,x)'?

Is it everything?
'[-inf,+inf]'?

Is it really meaningfully distinct from NULL?

Where do you see it being useful?

-Kevin

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