Certs are there to show that you have a good grasp of certain concepts, not as learning tools.
Something like O'Reilly's High-Performance MySQL book would be a great way to get the knowledge part down, but nothing beats hands-on experience.
Cool right? I read about it in this book, which is 10 years old!
I was kind of thrown into MySQL for trial by fire. The company that I worked at as an Operations Engineer needed someone to focus on the databases. I volunteered and, through learning as I went, I picked up a lot.
I recommend a few things. First of all, pick up High Performance MySQL. It is a great read and will give you some very useful insights as to how MySQL operates internally. I think I have 4 or 5 copies sitting around the house.
Next, download the Sakila database. Poke around in there and see what you can find. Google "Sakila Database Exercises" and I'm sure you will find a lot of exercises to do on that dataset.
Personally, I learn best two ways. First, by trial and error. I have to get my hands in a system and try things to see what works, how it works and so on. Next, I learn from other people. Don't be afraid to google and ask about things. There are TONS of resources out there to help people learn mysql.
High Performance MySQL is a good place to start.
Depending on what you're doing with MySQL, you may also want to check out VividCortex, the monitoring tool designed by Baron Schwartz, one of the authors of that book.
Give VividCortex a look too, specifically for database monitoring. VividCortex offers the most granular monitoring available (constant 1 second granularity), which is pretty crazy and extremely useful. It was also founded and is run by Baron Scwartz, who literally wrote <em>the</em> book on MySQL. You can also watch a video of the app in action, if you're interested.
When you get to a project larger than a small business or personal website it's less about the language and more about imposing a structure that makes sense backed by a data model that's thought out and performant.
I recommend these books:
http://www.amazon.com/High-Performance-MySQL-Optimization-Replication/dp/1449314287/ref=sr_1_1?ie=UTF8&qid=1425831227&sr=8-1&keywords=high+performance+mysql http://www.amazon.com/gp/product/0321127420/ref=oh_aui_detailpage_o05_s00?ie=UTF8&psc=1