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Re: Range types

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Jeff Davis <pgsql(at)j-davis(dot)com>
Cc: Scott Bailey <artacus(at)comcast(dot)net>, hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Range types
Date: 2009-12-14 19:23:38
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Lists: pgsql-hackers
Jeff Davis <pgsql(at)j-davis(dot)com> writes:
> On Mon, 2009-12-14 at 13:32 -0500, Tom Lane wrote:
>> The main question I would have is how to tell whether the underlying
>> type is really discrete.

> We can ask the user to provide a prior() and next() function, and if
> they aren't provided, we assume it's continuous.

Well, that still leaves us with the problem that Joe Schmo will file
a bug when "create function next(float4) returns float4 as
$$ select $1 + 0.00001 $$" doesn't behave sanely for him.  I'd prefer
not to leave it to the user to decide whether a type is discrete or
not.  The traffic on pgsql-bugs is convincing evidence that a very
large fraction of our user-base doesn't understand that floats are
inexact :-(

> I think "countable" is a more accurate word than "discrete". Strings are
> discrete but not countable.

It's been too long since college math classes for me to be sure whether
"discrete" is really the exact term here.  But I'm even more suspicious
of "countable".  I think a suitable diagonalization argument might show
that strings are countable.  That's getting a bit off-topic though...

			regards, tom lane

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