X-Original-To: pgsql-sql-postgresql.org@localhost.postgresql.org Received: from localhost (unknown [200.46.204.144]) by svr1.postgresql.org (Postfix) with ESMTP id 2750CD1B74B for ; Fri, 25 Jun 2004 02:37:52 -0300 (ADT) Received: from svr1.postgresql.org ([200.46.204.71]) by localhost (av.hub.org [200.46.204.144]) (amavisd-new, port 10024) with ESMTP id 96257-10 for ; Fri, 25 Jun 2004 05:37:51 +0000 (GMT) Received: from mproxy.gmail.com (mproxy.gmail.com [216.239.56.251]) by svr1.postgresql.org (Postfix) with SMTP id 6B25AD1B297 for ; Fri, 25 Jun 2004 02:37:48 -0300 (ADT) Received: by mproxy.gmail.com with SMTP id x43so222198cwb for ; Thu, 24 Jun 2004 22:37:45 -0700 (PDT) Received: by 10.38.181.8 with SMTP id d8mr36085rnf; Thu, 24 Jun 2004 22:37:45 -0700 (PDT) Message-ID: <37d451f70406242237dce4a8e@mail.gmail.com> Date: Fri, 25 Jun 2004 00:37:45 -0500 From: Rosser Schwarz To: pgsql-sql@postgresql.org Subject: Re: feature request ? In-Reply-To: <200406250816.47781.sad@bankir.ru> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit References: <200406250816.47781.sad@bankir.ru> X-Virus-Scanned: by amavisd-new at hub.org X-Spam-Status: No, hits=0.0 tagged_above=0.0 required=5.0 tests= X-Spam-Level: X-Archive-Number: 200406/250 X-Sequence-Number: 18195 On Fri, 25 Jun 2004 08:16:47 +0400, sad wrote: > > Very simply, a boolean may have to values: true or false. It's also > > possible that it's not been set to anything (NULL). > really ? > what about (13 < NULL)::BOOL Per the semantics of NULL, 13 is neither greater than nor less than NULL. NULL is the *unknown* value; it's impossible to meaningfully compare it to anything else. Try (NULL = NULL)::boolean. It's NULL, also. Since no value, including NULL, is in any way definitively comparable to NULL -- the unknown value -- comparing to NULL results in ... unknown. Otherwise known as NULL. /rls -- :wq