Re: modeling either/or relationship...

David Portas wrote:
> I think the different tables for 2- and 4-door vehicles was a poorly
> chosen example - useful only to illustrate how to extend the design.
> The number of doors is an attribute that all vehicles have in common so
> it more sensibly belongs in one place only - the Vehicles table.
>
> More generally, a union and joins should allow you to interrogate the
> data across all tables without resorting to procedural code in an
> external script.
>
> --
> David Portas

Thanks for your response. Simplifying it slightly, if I wanted to determine the total number of cars stored, the logical process might be:

1. Obtain the table names for individual car types (SUV, SED, etc) from the master table (so I can determine where the cars are stored).
2. Iterate through each of these type names counting the no. of rows in each of their corresponding sub table.
3. Sum these counts.

But how to link these steps together into one statement is still eluding me, specifically the link between steps 1 and 2? Much appreciated if anyone can illuminate me. Many thanks, Jason. Received on Wed Feb 01 2006 - 14:14:08 CET