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From: Erik Thiele <[email protected]>
To: Bruno Wolff III <[email protected]>
Cc: [email protected]
Subject: Re: special integrity constraints
Date: Mon, 22 Mar 2004 17:21:21 +0100
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
References: <[email protected]>
	<[email protected]>
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	<[email protected]>

On Mon, 22 Mar 2004 09:12:11 -0600
Bruno Wolff III <[email protected]> wrote:

> On Mon, Mar 22, 2004 at 14:10:42 +0100,
>   Erik Thiele <[email protected]> wrote:
> > 
> > it means (((count_rows(a)+count_rows(b)) modulo 2) == 0)
> 
> OK, that means my FK suggestion won't help. The other suggestion about
> putting triggers on "a" and "b" to update a count in another table
> that has a deferred check constraint on it may be your best bet.
> This will be a source of contention, but that may or may not be all
> that important depending on how often you are updating "a" and "b".
> 

there is no such thing as a deferred check constraint:

DEFERRABLE
NOT DEFERRABLE

This controls whether the constraint can be deferred. A constraint that
is not deferrable will be checked immediately after every command.
Checking of constraints that are deferrable may be postponed until the
end of the transaction (using the SET CONSTRAINTS command). NOT
DEFERRABLE is the default. 

!!! Only foreign key constraints currently accept
this clause. All other constraint types are not deferrable. !!!


cu
erik

-- 
Erik Thiele

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