From: Jan Wieck <JanWieck@Yahoo.com>
To: olly@lfix.co.uk
Cc: Josh Berkus <josh@agliodbs.com>
Cc: pgsql-sql@postgresql.org
Subject: Re: multi column foreign key for implicitly unique columns
Date: Thu, 19 Aug 2004 17:41:07 -0400
Message-ID: <41251E73.6070001@Yahoo.com> (raw)
In-Reply-To: <1092934366.19834.88.camel@braydb>
References: <1092734724.2627.4.camel@dicaprio.akademie1.de>
<200408181155.34472.josh@agliodbs.com>
<4123D91D.8060601@Yahoo.com>
<200408190921.59529.josh@agliodbs.com>
<1092934366.19834.88.camel@braydb>
On 8/19/2004 12:52 PM, Oliver Elphick wrote:
> On Thu, 2004-08-19 at 17:21, Josh Berkus wrote:
>> Jan,
>>
>> > Because the value in b.y is redundant. b.x->a.x->a.y is exactly the same
>> > value and he even wants to ensure this with the constraint.
>>
>> And in the absence of that constraint, what ensures that b.y = a.y, exactly?
>
> In the absence of b.y, it would be impossible for it to be anything
> else. Isn't that the point?
Precisely. I meant that the entire column is redundant and obsolete.
Without the column, no need for any constraint.
> It seems to me that he was trying to use the database to show errors in
> his source data, but since his constraint would reject the data, he
> wouldn't be able to enter it; all he could do would be to see the
> error. So he might as well turn it round, normalise the data properly
> and use the database to tell the rest of the system what the data ought
> to be.
I assumed he often queries b, and to avoid joining a all the time he
duplicates values from a into b and then tries to ensure that they stay
in sync with constraints.
Jan
--
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To: pgsql-sql@postgresql.org
Cc: JanWieck@Yahoo.com, olly@lfix.co.uk, josh@agliodbs.com
Subject: Re: multi column foreign key for implicitly unique columns
In-Reply-To: <41251E73.6070001@Yahoo.com>
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