Received: from maia.hub.org (maia-2.hub.org [200.46.204.251]) by mail.postgresql.org (Postfix) with ESMTP id 906D21337BD9 for ; Wed, 27 Apr 2011 05:47:13 -0300 (ADT) Received: from mail.postgresql.org ([200.46.204.86]) by maia.hub.org (mx1.hub.org [200.46.204.251]) (amavisd-maia, port 10024) with ESMTP id 28741-03-3 for ; Wed, 27 Apr 2011 08:46:55 +0000 (UTC) X-Greylist: from auto-whitelisted by SQLgrey-1.7.6 Received: from smarthost01.mail.zen.net.uk (smarthost01.mail.zen.net.uk [212.23.3.140]) by mail.postgresql.org (Postfix) with ESMTP id 016A51337C06 for ; Wed, 27 Apr 2011 05:46:43 -0300 (ADT) Received: from [82.68.43.86] (helo=mail.douglastechnology.co.uk) by smarthost01.mail.zen.net.uk with esmtp (Exim 4.63) (envelope-from ) id 1QF0ON-00039b-TV for pgsql-docs@postgresql.org; Wed, 27 Apr 2011 08:46:40 +0000 Received: from [192.168.16.200] (unknown [192.168.16.200]) by mail.douglastechnology.co.uk (Postfix) with ESMTPSA id 5C52B1264538 for ; Wed, 27 Apr 2011 09:46:39 +0100 (BST) Message-ID: <4DB7D7E3.6010403@douglastechnology.co.uk> Date: Wed, 27 Apr 2011 09:46:27 +0100 From: Jack Douglas User-Agent: Mozilla/5.0 (Windows; U; Windows NT 6.1; en-GB; rv:1.9.2.15) Gecko/20110303 Lightning/1.0b2 Thunderbird/3.1.9 MIME-Version: 1.0 To: pgsql-docs@postgresql.org Subject: boolean states Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-Originating-Smarthost01-IP: [82.68.43.86] X-Virus-Scanned: Maia Mailguard 1.0.1 X-Spam-Status: No, hits=-1.9 tagged_above=-5 required=5 tests=BAYES_00=-1.9, RCVD_IN_DNSWL_NONE=-0.0001 X-Spam-Level: X-Archive-Number: 201104/97 X-Sequence-Number: 6668 Hi http://www.postgresql.org/docs/current/static/datatype-boolean.html states: The boolean type can have one of only two states: "true" or "false". A third state, "unknown", is represented by the SQL null value. This sounds like an oxymoron to me. Perhaps that sentence should be changed to: The boolean type can have one of three states: "true" or "false" and "unknown". The third state, "unknown", is represented by the SQL null value. or: The boolean type can have one of three states: "true" or "false" and null. The third state, null, represents the logical value "unknown". Best regards Jack Douglas