From: Jan Wieck <JanWieck@Yahoo.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Richard Huxton <dev@archonet.com>
Cc: Markus Bertheau <twanger@bluetwanger.de>
Cc: Josh Berkus <josh@agliodbs.com>
Cc: olly@lfix.co.uk, pgsql-sql@postgresql.org, Bruce Momjian <pgman@candle.pha.pa.us>
Subject: Re: multi column foreign key for implicitly unique columns
Date: Wed, 18 Aug 2004 14:01:52 -0400
Message-ID: <41239990.1000007@Yahoo.com> (raw)
In-Reply-To: <1803.1092847586@sss.pgh.pa.us>
References: <1092734724.2627.4.camel@dicaprio.akademie1.de>
<1092735576.28365.48.camel@linda>
<1092736197.2627.12.camel@dicaprio.akademie1.de>
<200408171945.15663.josh@agliodbs.com>
<41235A90.1080300@Yahoo.com>
<1092836961.2630.3.camel@dicaprio.akademie1.de>
<41236277.5060903@Yahoo.com>
<22808.1092842209@sss.pgh.pa.us>
<41237DA2.9090405@archonet.com>
<1535.1092845917@sss.pgh.pa.us>
<4123837C.30408@Yahoo.com>
<1803.1092847586@sss.pgh.pa.us>
On 8/18/2004 12:46 PM, Tom Lane wrote:
> Jan Wieck <JanWieck@Yahoo.com> writes:
>> If we allow for a unique index, that
>> * it is NOT maintained (no index tuples in there)
>> * depends on another index that has a subset of columns
>> * if that subset-index is dropped, the index becomes maintained
>> then the uncertainty is gone. At the time someone drops the other
>> constraint or unique index, the data is unique with respect to the
>> superset of columns. So building the unique index data at that time will
>> succeed.
>
> My goodness this is getting ugly. The notion of having to invoke an
> index build as a side-effect of a DROP sounds like a recipe for trouble.
The idea sure needs some refinement :-)
> I'd like to see more than one person needing it, before we go to that
> kind of trouble to do something that's not in the spec.
Actually, the whole thing strikes me more as a sign for a denormalized
database schema.
If a.x is unique, then (b.x, b.y) references (a.x, a.y) is only ensuring
that the redundant copy of y in b.y stays in sync with a.y.
Jan
--
#======================================================================#
# It's easier to get forgiveness for being wrong than for being right. #
# Let's break this rule - forgive me. #
#================================================== JanWieck@Yahoo.com #
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To: pgsql-sql@postgresql.org
Cc: JanWieck@Yahoo.com, tgl@sss.pgh.pa.us, dev@archonet.com, twanger@bluetwanger.de, josh@agliodbs.com, pgman@candle.pha.pa.us
Subject: Re: multi column foreign key for implicitly unique columns
In-Reply-To: <41239990.1000007@Yahoo.com>
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