Russi,
I can highly recommend a book - SAMS Teach Yourself SQL in 24 hours (2nd Edition). Most of the examples are oracle, but they also show examples from Sybase, SQL Server and dBase. Very good explanation, break-down, examples and exercises. You need to be a little wary as I recall some of the answers in the back being incorrect (typos or just plain wrong), but it was a good resource anyway... and I still use it as a refresher. All examples can be entered into your database to physically test using the set-up described in the back of the book.
James