To: Craig Ringer <craig@postnewspapers.com.au>
cc: Pavel Stehule <pavel.stehule@gmail.com>,
	Ivan Sergio Borgonovo <mail@webthatworks.it>, pgsql-sql@postgresql.org
Subject: Re: short-cutting if sum()>constant 
In-reply-to: <4B323F21.3020007@postnewspapers.com.au> 
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	<162867790912221147r7e3041fej44332a05faf915d6@mail.gmail.com>
	<20091223000031.54ad09b5@dawn.webthatworks.it>
	<20091223010940.51c5c069@dawn.webthatworks.it>
	<20091223024635.48d66554@dawn.webthatworks.it>
	<162867790912222338v73261b73u5c4e88a5ce85918f@mail.gmail.com>
	<20091223115628.1709caf5@dawn.webthatworks.it>
	<162867790912230352v5b6e395fm1880111c04eaa626@mail.gmail.com>
	<4B323F21.3020007@postnewspapers.com.au>
Comments: In-reply-to Craig Ringer <craig@postnewspapers.com.au>
	message dated "Thu, 24 Dec 2009 00:02:41 +0800"
Date: Wed, 23 Dec 2009 11:36:31 -0500
Message-ID: <28619.1261586191@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>

Craig Ringer <craig@postnewspapers.com.au> writes:
> Pavel Stehule wrote:
>> these queries are executed in some special mode, but still it is more
>> expensive than C a = a + 1

> ... and may have different rules, so you can't just write a simple "map
> expressions to C equivalents" arithmetic evaluator.

Yeah.  As an example, overflow is supposed to be caught in "a + 1",
unlike what would happen in C.

In principle you could map some of the builtin operators into inline
code, but it would be a great deal of work and the results would be
un-portable.

			regards, tom lane