If you are still in a search of how to improve your SQL skills, here is a list of the top three SQL boot camps for FREE that will help you get started with Oracle Database and SQL. All you need is an Oracle Account to take the class. 

Databases for Developers: Foundations  Now you can Learn SQL for FREE with the help of this 12-part boot camp. It will help you get started with Oracle Database and SQL. The course is a series of videos to teach you database concepts, interactive SQL tutorials, and quizzes to reinforce the ideas. Complete the course to get your free certificate. Course reviews:  “The videos were very well done: funny and interesting. the most useful part was the theory written in the Live SQL section of each module”

Databases for Developers: Performance If you want to learn how to make SQL faster join this FREE 10-part boot camp. The course is a series of videos to teach you performance concepts, interactive SQL tutorials, and quizzes to reinforce the ideas. You’ll learn how to get and read execution plans, create indexes and materialized views, find slow SQL, and other key performance tuning techniques. Course reviews: “This is an excellent hands-on class. I’ve learned a lot from it and thank you for doing a great class.”

Databases for Developers: Next Level  This is a FREE 10-part tutorial to help you improve your Oracle SQL skills. This course continues where Databases for Developers: Foundations left off, taking you further on your SQL journey. The class consists of a series of videos introducing concepts, interactive coding sections, and quizzes to test your understanding. The first module is now open. Course reviews: “Great content presented casually but thoroughly”.