Message-ID: <40B593BA.6090502@gmx.net>
Date: Thu, 27 May 2004 09:07:38 +0200
From: Andreas <maps.on@gmx.net>
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To: Jean-Luc Lachance <jllachan@sympatico.ca>
Cc: pgsql-sql@postgresql.org
Subject: Re: Multitable uniqueness ?
References: <40B40B4A.4050908@gmx.net> <40B4A2FD.8030004@sympatico.ca>
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Jean-Luc Lachance schrieb:

> Do you really need MANY-TO-MANY between customers and projects?
> I can see customers owning many projects, but do you really have 
> projects belonging to many customers?

In this case yes.
projects (
   1, 'x-fair 2003';
   2, 'y-fair 2003';
   3, 'x-fair 2004')

customer (
   1, 'X ltd';
   2, 'Y';
   3, 'Z')

maybe all 3 have a stall on project 1.
c1 and c2 attend project 2 where c2 has 2 stalls one inside and one 
outside the hall.

I have the cust_project relation to tie other objects like proposals and 
letters to something small and common for all the communication to a 
customer.

> If not, fold cust_proj into projects.
> Otherwise, UNIQUE (cp_id, stall_no) on stalls should be enough.


cp_id implies uniquness of (customer, project) couples.
So with UNIQUE (cp_id, stall_no) we get
--> UNIQUE (c_id, p_id, stall_no)
This'd be too much. Stall_no is the number of the cubicles the customers 
rent.
It needs to be unique within on project so that we can relate on a 
specific spot on the area to send visitors when they ask us and we print 
those numbers in the flyer.