Did you know there is a free GYM that lets you work on forms. There are even quizzes to help you test your knowledge. This is part of the Oracle Gym and I started the Normally Normalized: Third Normal Form workout.
You will need an Oracle login which is free and each workout is short. Actually the two supporting documents and the three quizzes are each 5-6 minutes so in a half an hour you can complete the entire workout, or save each part by itself over a longer time period.
Other Courses are available such as deductive logic, PL/SQL, and knowing the difference between RANGE and ROWS in a windowing function. Now most of these workout are designed for the Oracle database but the concepts usually fir very well with MySQL too. While me MySQL-ers may not need to use PL/SQL the materials on the higher level concepts are invaluable and the quizzes are going to make you think.
So if you are looking for a challenge or need a quick workout, please check out the Oracle Gym.