Most important when doing your reading on relational databases is learning how to normalize your database tables. Having a good normalized database gives you improved performance, a robust design and is also easy to maintain.

Have a look at Basics, First Normal Form, Second Normal Form, Third Normal Form and Fourth Normal Form.

This is also a good place to start: it has a lot of further links.

CountZero

"If you have four groups working on a compiler, you'll get a 4-pass compiler." - Conway's Law