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On the subject of inheritance

From: Martin Foster <martin(at)ethereal-realms(dot)org>
To: PostgreSQL Novice List <pgsql-novice(at)postgresql(dot)org>
Subject: On the subject of inheritance
Date: 2006-04-14 21:49:33
Message-ID: 444018ED.5030403@ethereal-realms.org (view raw or flat)
Thread:
Lists: pgsql-novice
I have been looking at documentation on inheritance and am not overly 
clear on all aspects of it.  Fortunately, the examples in 'PostgreSQL' 
from 'Developers Library' showed examples which were helpful however I 
am still curious if it would work for my circumstance.

I have a table which is used throughout the site and tracks users. 
This information is what is required by the scripts to establish 
identity, authenticate and correspond with off site.  e.g.

USER
   UserName  VARCHAR(10)
   UserPass  VARCHAR(12)
   UserEmail VARCHAR(30)


There is a new aspect to the site which is completely optional and seems 
like a good candidate for inheritance of the user table.    Simply put, 
these additional attributes ADDITIONAL would be in a separate table 
applied to and used only when necessary.   This brings me to my questions.

OPTIONAL (Inherits from USER)
   OptionalFirstName VARCHAR(15)
   OptionalLastName  VARCHAR(15)
   OptionalAddress   VARCHAR(45)
   OptionalPhone     VARCHAR(15)

First of all, does a row created in the USER table appear in the 
OPTIONAL table which inherits from it?   Meaning could I add in the 
optional attributes at a later time using a simply ALTER TABLE OPTIONAL 
statement when the UserName exists in USER?

Secondly, if the above is not possible does this require me to recreate 
the entry from USER into OPTIONAL?  And if so, what exactly happens? 
Are there two records now or just one?  Would I get a referential 
integrity error and what would happened if the entry in USER was removed 
would it be ripped from OPTIONAL as well?

Any clarification on this would be appreciated!

	Martin Foster
	martin(at)ethereal-realms(dot)org


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Subject: Re: On the subject of inheritance
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