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

> "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