Received: from makus.postgresql.org (makus.postgresql.org [98.129.198.125])
	by mail.postgresql.org (Postfix) with ESMTP id 77FFBF6B3CB
	for <pgsql-sql@postgresql.org>; Thu, 19 Apr 2012 15:30:50 -0300 (ADT)
Received: from mail-pb0-f46.google.com ([209.85.160.46])
	by makus.postgresql.org with esmtp (Exim 4.72)
	(envelope-from <robjsargent@gmail.com>) id 1SKw81-0005uz-BX
	for pgsql-sql@postgresql.org; Thu, 19 Apr 2012 18:30:50 +0000
Received: by pbcun15 with SMTP id un15so93757pbc.19
	for <pgsql-sql@postgresql.org>; Thu, 19 Apr 2012 11:30:36 -0700 (PDT)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113;
	h=message-id:date:from:user-agent:mime-version:to:subject:references
	:in-reply-to:content-type:content-transfer-encoding;
	bh=wNdVzdvhPUcqcGbuIFPST17uaAWZnx/HcX0bonDSuiM=;
	b=02M5mB00M/DbPlRimmzfaZrIpJw9VhmsHv9GOqClK6bFs8XlG9vPDYImok8BVH7bVN
	GmISvR0HkdjUPdFBLrIzidoUbqcosEwHGZ0qEKB69AxBX720b2OVOnkw/YdEGUpSnXNC
	rHKT6cq6NZ+Po5aH9twoMLArXDESwZL7RW+wEnsotyH/BGzVyX6ESFkgY6O4tOS/Iq5M
	FXCOyBllyDERg8DB8HJIlLOrhi4BV+6qkWRVFsoX4G52MLVqPpRix+sV4HuxvE9ypKea
	4U8AiqQleloff5zFzxAKKX8cYI9kBRKm1y+zxT/6GftzMCN6YLUWRKSCrCJUlCouxlJa
	Gsww==
Received: by 10.68.224.228 with SMTP id rf4mr6391331pbc.22.1334860236599;
	Thu, 19 Apr 2012 11:30:36 -0700 (PDT)
Received: from [172.16.1.88] ([208.187.158.94])
	by mx.google.com with ESMTPS id a9sm2898691pbo.48.2012.04.19.11.30.34
	(version=SSLv3 cipher=OTHER); Thu, 19 Apr 2012 11:30:35 -0700 (PDT)
Message-ID: <4F905A2F.7080205@gmail.com>
Date: Thu, 19 Apr 2012 12:32:15 -0600
From: Rob Sargent <robjsargent@gmail.com>
User-Agent: Mozilla/5.0 (X11; Linux x86_64;
	rv:11.0) Gecko/20120329 Thunderbird/11.0.1
MIME-Version: 1.0
To: pgsql-sql@postgresql.org
Subject: Re: Uniform UPDATE queries
References: <4F8E936A.9050303@victorem.com> <4420.1334766267@sss.pgh.pa.us>
	<4F8FEF2D.6050501@victorem.com>
In-Reply-To: <4F8FEF2D.6050501@victorem.com>
Content-Type: text/plain; charset=windows-1252; format=flowed
Content-Transfer-Encoding: 7bit
X-Pg-Spam-Score: -2.6 (--)
X-Archive-Number: 201204/43
X-Sequence-Number: 36520

On 04/19/2012 04:55 AM, Dennis wrote:
> Hello Tom,
>
> The example you have given is EXACTLY why something like CURRENT is
> needed to limit the number of unique queries or prepared statements. (or
> to do a selection of all values before an update meaning two executed
> queries.)
>
> regards,.
>
> Dennis
>
> On 04/18/2012 06:24 PM, Tom Lane wrote:
>> Dennis<dennis.verbeek@victorem.com> writes:
>>> When a query is written to update a table, the usual process is to
>>> list all the columns that need
>>> updating. This could imply the creation of many possible queries for
>>> many columns. In an effort to
>>> keep the UPDATE queries more uniform, less number of unique queries,
>>> a keyword similar to DEFAULT,
>>> let's say CURRENT, is required to indicate that the current value
>>> must not change.
>> No it isn't. Just write the name of the column, eg
>>
>> update mytable set x = x, y =<new value>, z = z where ...
>>
>> There's no reason to invent nonstandard syntax for this.
>>
>> regards, tom lane
>>
>>
>>
>
>


Not if you have all the old and new values:


update mytable set x= xval, y=yval, z=zval where yval happens to be a 
new value and xval, zval are current.

Seems your callers knows which have changed. Does it not know which have 
not (and what their values are)?