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From: Josh Berkus <josh@agliodbs.com>
Organization: Aglio Database Solutions
To: vwu98034@lycos.com, pgsql-sql@postgresql.org
Subject: Re: Inheritance or no inheritance, there is a question
Date: Mon, 18 Aug 2003 21:36:39 -0700
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Vernon,

> What is the best solution for this DB scheme problem?

Have you considered not using inheritance?   As a relational-SQL geek myself, 
I'm not keen on inheritance -- I feel it mucks up the relational model.  Not 
everyone agrees with me, of course.

Personally, I'd suggest the following structure:

Profile A
	id Primary Key
	detail1
	detail2

Profile B
	id Primary Key references Profile A ( ID )
	detail 3
	detail 4
	detail 5

Profile Languages
	id not null references profile A ( ID )
	language id
	primary key id, language id

etc.

In this way, Profile B is a child table with a 1:0-1 relationship with Profile 
A.  Multi-value dependancies, like Languages, can be related to either the 
people who belong to the B group (and, by implication, the B group) or the 
people who belong to the A group only.

Want the B group?  SELECT A JOIN B
Want the A group only?  SELECT A EXCEPT B

This is the "relational" way to approach the problem.

-- 
Josh Berkus
Aglio Database Solutions
San Francisco