Re: modeling either/or relationship...

David Portas wrote:
> jason.glumidge_at_gmail.com wrote:
>
> > 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.
>
> How about:
>
> SELECT COUNT(*) FROM Vehicles;
>
> Or maybe:
>
> SELECT COUNT(*)
> FROM Vehicles
> WHERE vehicle_type IN
> (... list of types);
>
> --
> David Portas

My bad. By simplifying and not actually thinking, I trivialised the example to a simple select statement, and lost my real question - I think I'll quit while I'm behind ;) Thanks for attempting to answer the question anyhow. Received on Wed Feb 01 2006 - 15:22:17 CET