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From: Robert Haas <[email protected]>
To: Grzegorz Szpetkowski <[email protected]>
Cc: [email protected]
Subject: Re: 5.3.5. Foreign Keys (The SQL Language) possible enhance
Date: Thu, 19 May 2011 16:17:10 -0400
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
References: <[email protected]>

On Fri, May 6, 2011 at 9:50 PM, Grzegorz Szpetkowski
<[email protected]> wrote:
> I have some remark about
>
> "Now it is impossible to create orders with product_no entries that do
> not appear in the products table."
>
> http://www.postgresql.org/docs/9.0/static/ddl-constraints.html#DDL-CONSTRAINTS-FK
[...]
>
> There is still possibility to add product_no (exactly NULL) value,
> which does not appear (cannot because of primary key nature) in
> products table. To get "full solution" you need create orders table as
>
> CREATE TABLE orders (
>    order_id integer PRIMARY KEY,
>    product_no integer REFERENCES products (product_no) NOT NULL,
>    quantity integer
> );

I don't think we should change the example, but we could probably
clarify the wording.

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

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