Re: Precedence of standard comparison operators

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Kevin Grittner <kgrittn(at)ymail(dot)com>
Cc: "pgsql-hackers(at)postgreSQL(dot)org" <pgsql-hackers(at)postgreSQL(dot)org>
Subject: Re: Precedence of standard comparison operators
Date: 2015-02-20 17:04:53
Message-ID: 23431.1424451893@sss.pgh.pa.us
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Kevin Grittner <kgrittn(at)ymail(dot)com> writes:
> I have a memory of running into this in real-world production code
> and that it involved booleans. I'll see whether I posted something
> to the community lists about it, but it didn't take long to produce
> an (admittedly artificial) case where incorrect results are
> silently returned:

> test=# select 'f'::boolean = 'f'::boolean >= 'f'::boolean;
> ?column?
> ----------
> f
> (1 row)

> test=# select 'f'::boolean >= 'f'::boolean >= 'f'::boolean;
> ?column?
> ----------
> t
> (1 row)

One of the reasons I want to make these operators %nonassoc is
so you get an error on cases like these --- if you actually meant
this, you'll be forced to parenthesize one way or the other.

regards, tom lane

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