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Re: Multiway associations

From: Michael Glaesemann <grzm(at)myrealbox(dot)com>
To: Russell Shaw <rjshaw(at)iprimus(dot)com(dot)au>
Cc: pgsql-novice(at)postgresql(dot)org
Subject: Re: Multiway associations
Date: 2004-01-25 06:33:21
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Lists: pgsql-novice
On Jan 25, 2004, at 2:23 PM, Russell Shaw wrote:

> Michael Glaesemann wrote:
>> Hi Russel
>> On Jan 25, 2004, at 12:46 PM, Russell Shaw wrote:
>>> I have a list of parts, each of which is sold by multiple
>>> vendors. I also have a list of vendors, each of which sell
>>> multiple parts.
>>> How should i arrange the tables for this that doesn't involve
>>> having lots of empty fields "just in case" ?
>> One common way to do this is to have three tables: one suppliers, one 
>> parts, and one suppliers-parts referencing suppliers and parts.
> Hi,
>> Does that help?
> Maybe so. I thought of this and was wondering if it was the common 
> solution.
> Should it be something like:
> spid  supplier  part
> ---------------------
> 0     sid_1     pid_1
> 1     sid_1     pid_2
> 2     sid_2     pid_2
> 3     sid_3     pid_3
> 4     sid_3     pid_1
> ...
> Ie, the third table just stores all the combinations of parts and 
> suppliers?

Yup. The spid might be superfluous, depending on what you need your 
database for. I've never needed one. You're probably only going to be 
doing queries like

SELECT part FROM suppliers_parts WHERE suppplier = sid_1

or variants of these. Probably will never touch the spid column. 
(Unless of course you have a particular reason for doing so :)

Michael Glaesemann
grzm myrealbox com

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