DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma;
	h=mime-version:in-reply-to:references:from:date:message-id:subject:to
	:cc:content-type;
	b=erhtMt8svYPHZtR7JMkXvGUoyVBxSV694mtkZMLr0C+nI0WKPD5iaqPH7mEGtYzgSI
	K3QZwLDEJZPO+vsQsfr7Sq5IwgpgwjiqcjOmB3Ev3QskXjmfX2a2V3EyIW/wlfR4Xblf
	1buMTMbyophTOKJLkWDFLpfsdJd3DI9VOVOe8=
MIME-Version: 1.0
In-Reply-To: <4DBA68E9.5090302@douglastechnology.co.uk>
References: <4DB7D7E3.6010403@douglastechnology.co.uk>
	<BANLkTimyUsgA-DvFi+AweMB4XXogUaMhDA@mail.gmail.com>
	<4DBA68E9.5090302@douglastechnology.co.uk>
From: Josh Kupershmidt <schmiddy@gmail.com>
Date: Sun, 1 May 2011 19:07:10 -0400
Message-ID: <BANLkTi=hfidffvLMYwpSHcnO3UdGDiNmvQ@mail.gmail.com>
Subject: Re: boolean states
To: Jack Douglas <jack@douglastechnology.co.uk>
Cc: pgsql-docs@postgresql.org
Content-Type: multipart/mixed; boundary=000e0cd51872a5654004a23ef850

--000e0cd51872a5654004a23ef850
Content-Type: text/plain; charset=windows-1252
Content-Transfer-Encoding: quoted-printable

On Fri, Apr 29, 2011 at 3:29 AM, Jack Douglas
<jack@douglastechnology.co.uk> wrote:
> NULL is not unique to boolean, but UNKNOWN is - it would surely be wrong =
to
> have no mention of it at all on this page. This is because the boolean ty=
pe
> is the only one used to represent truth (or logical) values. One of the
> comments from the link you provided:
>
>> What=92s even more interesting is that for BOOLEAN they invented the key=
word
>> UNKNOWN and the 2003 standard states =93The null value of the boolean da=
ta
>> type is equivalent to the Unknown truth value.=94 So for BOOLEAN (and on=
ly
>> BOOLEAN AFAICT) you=92re supposed to say WHERE <boolean primary> IS [NOT=
]
>> UNKNOWN. And in the definition of =93literal=94, which is supposed to =
=93Specify a
>> non-null value=94, =93boolean literal=94 is equated to TRUE, FALSE or UN=
KNOWN (but
>> the latter is equivalent to a =93null value=94 a few pages later).

Ah, OK - I had forgotten about that SQL syntax. I do agree that this senten=
ce:
| A third state, "unknown", is represented by the SQL null value.

is particularly confusing, suggesting that "unknown" is a valid
boolean literal, on equal footing with "true" and "false".

We do document the use of IS [NOT] UNKNOWN already, see:
<http://www.postgresql.org/docs/current/interactive/functions-comparison.ht=
ml>

and IMO that page is the appropriate place for such discussion. So
maybe we just need a link to that page, and should strip out the
confusing sentence about "third state" entirely? Patch attached.

Josh

--000e0cd51872a5654004a23ef850
Content-Type: application/octet-stream; name="boolean_unknown.patch"
Content-Disposition: attachment; filename="boolean_unknown.patch"
Content-Transfer-Encoding: base64
X-Attachment-Id: f_gn6jon0q0
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--000e0cd51872a5654004a23ef850--