From: | Josh Berkus <josh(at)agliodbs(dot)com> |
---|---|
To: | Kevin Grittner <Kevin(dot)Grittner(at)wicourts(dot)gov> |
Cc: | Robert Haas <robertmhaas(at)gmail(dot)com>, Jeff Davis <pgsql(at)j-davis(dot)com>, 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 18:02:20 |
Message-ID: | 4D5579AC.4050707@agliodbs.com |
Views: | Raw Message | Whole Thread | Download mbox | Resend email |
Thread: | |
Lists: | pgsql-hackers |
> "empty range"
> =============
> Zero length?
> If so, is it fixed at some point, but empty?
> '(x,x)'?
> '[x,x)'?
Neither of the above should be possible, I think. The expression "(x"
logically excludes the expression "x)".
However, "[x,x]" would be valid, and would be a zero-length interval at
the point "x".
> Is it everything?
> '[-inf,+inf]'?
No, that's "everything" which is a different concept. The above also
ought to be possible, and overlap everything.
> Is it really meaningfully distinct from NULL?
Yes. NULL means "I don't know". If a range type IS NULL, then any
operation performed with it ought to be NULL. Hence:
IF y > x, THEN:
[x,x] << [y,z) == TRUE
[x,x] -|- (x,y] == TRUE
NULL << [y,z} IS NULL
[-inf,+inf] << [y,z) == FALSE
I can imagine using all of these constructs in actual applications. In
fact, I have *already* used [-inf,+inf]
--
-- Josh Berkus
PostgreSQL Experts Inc.
http://www.pgexperts.com
From | Date | Subject | |
---|---|---|---|
Next Message | David E. Wheeler | 2011-02-11 18:04:57 | Re: Careful PL/Perl Release Not Required |
Previous Message | Alex Hunsaker | 2011-02-11 18:01:37 | Re: Careful PL/Perl Release Not Required |