> > This is where it gets nasty. A customer may be a human being or a
> > company. I see different approaches here:
> > 1) keep customer tables separate, based on which type of customer it is
> > 2) create the customer table with a column specifying if we're dealing
> > with a human being or a company
> > 3) create the customer table with a FK for people and a FK for
> > companies, and decide on the customer type in the application based on
> > the presence of that key
> You're making it more complicated than it needs to be.
> A customer may be either a person or a company.
> Your customers table may contain columns that are the union of what is
> required for a person and what is requried for a company, plus of course
> enumerated value that indicates which the customer is and indirectly which
> columns are populated for a given row.
> Problem solved. Over time, several square millimeters on a disk wasted.
Back to "database design" class for you ;-)
Store in a table what you need to store, storing "which columns are
for a given row." is complete rubbish.
By retrieving data you should -know- what data it is, not having to retrieve
a value that indicates what the data actually means.
Database Workbench - tool for InterBase, Firebird, MySQL, NexusDB, Sybase
SQL Anywhere, Oracle & MS SQL Server
Database development questions? Check the forum!