you can use setup a foreign key constraint in your create table so that column is only populated when
there is a value which syncs to the referenced value
http://www.postgresql.org/docs/7.4/interactive/sql-createtable.html
Martin
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> To: pgsql-general@postgresql.org
> From: matt@tplus1.com
> Subject: [GENERAL] Foreign Key normalization question
> Date: Tue, 2 Sep 2008 19:14:17 +0000
>
> I'm building an app that has a customers table, a locations table, a
> products table, and a product_locations table.
>
> They make a diamond shape.
>
> The locations table and the products table each have a customer_id
> column that links back to the customers table.
>
> Then the product_locations table table has just two columns: a
> location_id column and a product_id column, each linking back to the
> appropriate table.
>
> I want to write a constraint or a trigger or something else that makes
> sure that before a (location_id, product_id) tuple is inserted into the
> product_locations table, the system verifies that the product links to
> the same customer as the location.
>
> How do I do this?
>
> Thanks in advance.
>
> Matt
>
>
>
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