Re: Foreign key to 2 tables problem

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От Achilleus Mantzios
Тема Re: Foreign key to 2 tables problem
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Msg-id Pine.LNX.4.44.0511221827300.24697-100000@matrix.gatewaynet.com
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Ответ на Foreign key to 2 tables problem  (Joost Kraaijeveld <J.Kraaijeveld@Askesis.nl>)
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O Joost Kraaijeveld έγραψε στις 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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