Date: Thu, 9 Aug 2018 15:09:13 -0400
From: Bruce Momjian <bruce@momjian.us>
To: KES <kes-kes@yandex.ru>
Cc: Tom Lane <tgl@sss.pgh.pa.us>,
	PostgreSQL-development <pgsql-hackers@postgresql.org>
Subject: Re: Typo in doc or wrong EXCLUDE implementation
Message-ID: <20180809190913.GB14011@momjian.us>
References: <153121527691.1408.5686988620817799073@wrigleys.postgresql.org>
 <20180807173659.GD7297@momjian.us>
 <31616681533725753@sas1-d856b3d759c7.qloud-c.yandex.net>
 <20180808130040.GA2611@momjian.us>
 <12107.1533736288@sss.pgh.pa.us>
 <37593701533809465@sas1-87f9feb8d943.qloud-c.yandex.net>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <37593701533809465@sas1-87f9feb8d943.qloud-c.yandex.net>
User-Agent: Mutt/1.5.23 (2014-03-12)
Precedence: bulk

On Thu, Aug 9, 2018 at 01:11:05PM +0300, KES wrote:
> Bruce:
> >Yes, it would work, but doing that only for equality would be
> >surprising
>  to many people
>
> Why surprising? It is
> [documented](https://www.postgresql.org/docs/current/static/sql-create
> table.html#sql-createtable-exclude):
> >If all of the specified operators test for equality, this is
> >equivalent to a UNIQUE constraint, although an ordinary unique
> >constraint will be faster.
>
> Thus the UNIQUE constraint is just particular case of exclusion
> constraint, is not?

Well, for me a UNIQUE constraint guarantees each discrete value is
unique, while exclusion constraint says discrete or ranges or geometric
types don't overlap.  I realize equality is a special case of discrete,
but having such cases be marked as UNIQUE seems too confusing.

-- 
  Bruce Momjian  <bruce@momjian.us>        http://momjian.us
  EnterpriseDB                             http://enterprisedb.com

+ As you are, so once was I.  As I am, so you will be. +
+                      Ancient Roman grave inscription +