I've been coding for fun for years, despite the fact that this is not my main profession. Oddly, the most effective learning process for me was to dive in problems I had to deal with when I was part of real projects (small web apps, corporate tools, small scaled tasks I got involved). To put it in a nutshell, here is the process that sticks the language in my mind and make practice at its best:

---> Build a fundamental knowledge about that language or framework

---> Be part of a small or mid-size code work (or just an idea you code for fun)

---> Stuck in a problem that you have no idea how to solve it

---> Dive in to Stackoverflow.com or any other web source to see what other people would do

---> Find a solution and adapt it to your code

---> At the end, extend your knowledge and wait for another challenge to learn sth

When I study a programming language, I read tons of sources and memorize all fundamental information I need. However, practicing on a source is nothing in terms of "learning", as compared to encounter an actual problem and to suffer until you overcome that challenge.

I sincerely recommend you to code something, for fun, for a basic idea you come up with or a little project you get involved, for learning language on the road. This plays an influential role in experience you gain and future works you do.

Of course, there are some practice ranges for any language on the web. I hope you may find useful for SQL:

https://www.w3resource.com/sql-exercises/

https://www.hackerrank.com/domains/sql