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Re: Multitable uniqueness ?

From: Andreas <maps(dot)on(at)gmx(dot)net>
To: Jean-Luc Lachance <jllachan(at)sympatico(dot)ca>
Cc: pgsql-sql(at)postgresql(dot)org
Subject: Re: Multitable uniqueness ?
Date: 2004-05-27 07:07:38
Message-ID: 40B593BA.6090502@gmx.net (view raw or flat)
Thread:
Lists: pgsql-sql
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.



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