I'm not sure if this is the level you're looking for, but if you need a better mental model of SQL, you should take a look at Jennifer Widom's course on Stanford Lagunita on Databases: https://lagunita.stanford.edu/courses/Engineering/db/2014_1/...

Starting from the relational model and going through SQL really makes the language make sense.

If this is too basic for you, then, at worst, you'll spend a few hours reviewing the basics and strengthening your foundation.