Man, thank you so much for creating this. You should find some way to monetize it. I thought I had a decent grasp of SQL before, but this is what really helped me grok it ... especially the consistent 'everything is table' lesson.
Oh and I had an idea for practicing deletions/insertions/updates & other behavior that you couldn't do on web: create an Electron app that uses a local db. I'd buy that in a heartbeat.