Code Wars isn't good for learning from zero as there is no training, it is more of a self challenge site. Code Wars does have a SQL track where you can do SQL challenges.
If you want to learn from scratch I recommend looking at Code Combat if you want a really gentle introduction, otherwise a course from Udemy by Jose Portilla, Andrew Mead, or Maximilian Schwarzmüller (most Udemy courses suck, but they are really good) or Code Academy.
Thanks very much for your answer Mark!