Lao,
The first thing to do is learn SQL. You will need a database to practice on. Since your goal is to learn Oracle too, Oracle is a good database to start with. I would say to use Oracle 10g rather than 9i since it is a more recent version. It doesn't really matter for a beginner though as the basic features work the same.
As for a book, I recommend "Expert Oracle Programming." You can read my
JavaRanch review of this book.