Forum OpenACS Development: Response to Book recommendations for learning database design?
Richard Barker, CASE Method Entity Relationship Modeling (Addison Wesley Publishing Company, 1990), clothbound; ISBN 0-201-41696-4.
The best discussion of database design with RDBMS I've seen has been the first half of the O'Reilly book, Oracle Design, by Dave Ensor and Ian Stevenson. The later part of the book gets into pretty esoteric aspects of building applications with Oracle, but the first half explains really basic and useful things like the up and downsides or concatenated keys. Very clearly written.
C. J. Date, An Introduction to Database Systems (Addison-Wesley Publishing Company, 1995), 839 pages; clothbound; ISBN 0-201-54329-X.
This book is a classic that you can sometimes get for $12 at used book stores, but it's fairly academic in its presentation, and it can be a lot of work to get the practical information you're after:
If you want to look farther afield check out the Applied Information Science Selected Bibliography.