From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
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To: | "David G(dot) Johnston" <david(dot)g(dot)johnston(at)gmail(dot)com> |
Cc: | Андрей Авакимов <aquarius1993(at)rambler(dot)ru>, "pgsql-sql(at)postgresql(dot)org" <pgsql-sql(at)postgresql(dot)org> |
Subject: | Re: PostgreSQL 9.5 operator precedence |
Date: | 2016-09-20 14:47:50 |
Message-ID: | 20513.1474382870@sss.pgh.pa.us |
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Lists: | pgsql-sql |
"David G. Johnston" <david(dot)g(dot)johnston(at)gmail(dot)com> writes:
> On Mon, Sep 19, 2016 at 11:02 PM, <aquarius1993(at)rambler(dot)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
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