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From: Vik Fearing <[email protected]>
To: 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 23:35:56 +0200
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
References: <[email protected]>
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On 09/08/18 21:09, Bruce Momjian wrote:
> 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.

One of the things I'm currently trying to implement is the WITHOUT
OVERLAPS for UNIQUE constraints.

See SQL:2016 section 11.7 <unique constraint definition>
-- 
Vik Fearing                                          +33 6 46 75 15 36
http://2ndQuadrant.fr     PostgreSQL : Expertise, Formation et Support

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