Message-ID: <439FF36F.1040004@moonwatcher.it>
Date: Wed, 14 Dec 2005 11:26:55 +0100
From: Gianluca Riccardi <ml-reader@moonwatcher.it>
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To: pgsql-sql@postgresql.org
Subject: Re: DB design and foreign keys
References: <439F0FE8.1050503@moonwatcher.it> <439F1A23.40202@archonet.com>
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[cut]

>
> It means what it says. You have defined table orders with a primary 
> key of (id,order_code). This means that the combination of 
> (id,order_code) must be unique. 


yes, that was my thought, and in that context, i thought it could be 
correct in order to have uniqueness for creating foreign keys

> So - these could all exist at the same time:
>  (1,1), (1,2), (2,1), (2,2)
> You could not then add another (1,2) combination.


yes, again, i thought that was the uniqueness i needed...

>
> Since id and order_code are both just automatically-generated numbers 
> in the orders table it doesn't add anything to make both of them part 
> of a primary-key. I would delete the id column altogether and just 
> have the order_code as the primary-key (since "order_code" carries 
> more meaning to a human than "id"). This means your order_items table 
> can then safely reference the order_code it wants to.


> HTH


sure it did, thanks for your response, best regards,
Gianluca Riccardi