Re: How to code a supertype subtype relationship

The two most common ways are the one that you are using and adding the columns of subtypes to the supertype table and allowing attributes of X for example to be null for a subtype Y.

<bogstonkott_at_netscape.net> wrote in message news:901972da.0403231405.2d4711b6_at_posting.google.com...
> Let's talk about supertype-subtype relationship. Here's the problem:
> I have to use a column in the supertype to find a corresponding
> subtype. Here's an example:
>
> Say we have a supertype, S, with three subtypes, X, Y, and Z. I add a
> row, R1, to supertype S. I now add a row to subtype Y that
> corresponds to the row R1 in supertype S.
>
> Later, I query row R1 in supertype S. I now have a problem: which
> subtype corresponds to R1 in S. X, Y, or Z? Well, I have solved this
> problem by adding a column to S that tells its type in this case Y.
> So, I look at the type column in R1 and then lookup the child row in
> subtype Y.
>
> Is there a better way to code this?
>
> How do other people work with a supertype-subtype relationship?
>
> bogston
Received on Tue Mar 23 2004 - 23:34:30 CET