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From: Bruce Momjian <[email protected]>
To: KES <[email protected]>
Cc: Tom Lane <[email protected]>
Cc: PostgreSQL-development <[email protected]>
Subject: Re: Typo in doc or wrong EXCLUDE implementation
Date: Thu, 9 Aug 2018 15:09:13 -0400
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
References: <[email protected]>
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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  <[email protected]>        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 +

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