From: Tom Lane <tgl@sss.pgh.pa.us>
To: "David G. Johnston" <david.g.johnston@gmail.com>
cc: =?UTF-8?B?0JDQvdC00YDQtdC5INCQ0LLQsNC60LjQvNC+0LI=?=
 <aquarius1993@rambler.ru>,
        "pgsql-sql@postgresql.org" <pgsql-sql@postgresql.org>
Subject: Re: PostgreSQL 9.5 operator precedence
In-reply-to: 
 <CAKFQuwbY1c1iUZGLzi5430tZN9==ozM7bh3uUXDfcbZ3KcRWew@mail.gmail.com>
References: <1474351364.271814.29325.2780@mail.rambler.ru>
 <CAKFQuwbY1c1iUZGLzi5430tZN9==ozM7bh3uUXDfcbZ3KcRWew@mail.gmail.com>
Comments: In-reply-to "David G. Johnston" <david.g.johnston@gmail.com>
	message dated "Tue, 20 Sep 2016 07:10:58 -0700"
Date: Tue, 20 Sep 2016 10:47:50 -0400
Message-ID: <20513.1474382870@sss.pgh.pa.us>
Precedence: bulk
Sender: pgsql-sql-owner@postgresql.org

"David G. Johnston" <david.g.johnston@gmail.com> writes:
> On Mon, Sep 19, 2016 at 11:02 PM, Андрей Авакимов <aquarius1993@rambler.ru>
>> The thing I don't understand is the error message that I receive:
>> select 1 is null = 2 is null;
>> -----------------------------
>> ERROR:  operator does not exist: boolean = integer
>> LINE 1: select 1 is null = 2 is null

> ​Your query reads:
> SELECT ( ( 1 IS (NULL = 2) ) IS NULL​

No, certainly not that --- IS isn't some sort of standalone operator,
rather IS NULL is an indivisible combination of tokens representing a
postfix operator.  The query's really getting parsed like this:

select ((1 is null) = 2) is null;

whereas the pre-9.5 interpretation was

select (1 is null) = (2 is null);

If you add those parentheses explicitly then your query will work fine
in either version.

			regards, tom lane


-- 
Sent via pgsql-sql mailing list (pgsql-sql@postgresql.org)
To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-sql