Re: How to quote the COALESCE function?

From: Kevin Grittner <kgrittn(at)gmail(dot)com>
To: Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>
Cc: Roman Scherer <roman(at)burningswell(dot)com>, Jerry Sievers <gsievers19(at)comcast(dot)net>, "pgsql-general(at)postgresql(dot)org >> PG-General Mailing List" <pgsql-general(at)postgresql(dot)org>
Subject: Re: How to quote the COALESCE function?
Date: 2016-04-04 21:49:06
Message-ID: CACjxUsMJCHcYjEcg+sQ+HoidEWFgi4LTumMUsDiaSxOZ=AVM-Q@mail.gmail.com
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On Tue, Mar 29, 2016 at 12:38 PM, Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com> wrote:

> The coalesce is one few functions implemented by special rule in
> PostgreSQL parser.

In the SQL standard the COALESCE feature is not listed as a
function; it is listed as one of the short forms of CASE
expression. While it has function-like syntax, thinking of it as a
function is semantically incorrect.

COALESCE(a, b)

is supposed to be semantically equivalent to:

CASE WHEN a is not null THEN a ELSE b END

Among other things, that means that this statement should not
generate a divide by zero error:

SELECT COALESCE(1, 1/0);

--
Kevin Grittner
EDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

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