| From: | Achilleus Mantzios <achill(at)matrix(dot)gatewaynet(dot)com> |
|---|---|
| To: | Joost Kraaijeveld <J(dot)Kraaijeveld(at)Askesis(dot)nl> |
| Cc: | "Pgsql-sql(at)postgresql(dot)org" <Pgsql-sql(at)postgresql(dot)org> |
| Subject: | Re: Foreign key to 2 tables problem |
| Date: | 2005-11-22 16:32:39 |
| Message-ID: | Pine.LNX.4.44.0511221827300.24697-100000@matrix.gatewaynet.com |
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| Thread: | |
| Lists: | pgsql-sql |
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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