From: Achilleus Mantzios <achill@matrix.gatewaynet.com>
To: Joost Kraaijeveld <J.Kraaijeveld@Askesis.nl>
Cc: Pgsql-sql@postgresql.org <Pgsql-sql@postgresql.org>
Subject: Re: Foreign key to 2 tables problem
Date: Tue, 22 Nov 2005 18:32:39 +0200 (EET)
Message-ID: <Pine.LNX.4.44.0511221827300.24697-100000@matrix.gatewaynet.com> (raw)
In-Reply-To: <1132673053.5701.9.camel@Panoramix>
O Joost Kraaijeveld Ýãñáøå óôéò Nov 22, 2005 :
> Hi,
>
> Is there a way to create a foreign key to 2 tables: e.g. a bankaccount
> table that has a column "owner", that must point to a record in either
> the customer or the supplier table?
While there are techniques to accomplish this,
i see a problem:
How do you know if a certain value in owner is to be joined
with e.g. customer and not supplier??
The right way is to have 2 columns that can be null,
pointing to customer,supplier respectively,
and then write a trigger to ensure that exactly one
is not null.
>
>
> TIA
>
>
--
-Achilleus
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Subject: Re: Foreign key to 2 tables problem
In-Reply-To: <Pine.LNX.4.44.0511221827300.24697-100000@matrix.gatewaynet.com>
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