I highly recommend the O'Reilly SQL Pocket Guide (https://www.oreilly.com/library/view/sql-pocket-guide/978149...). Its explanation of CTEs is fantastic, and it does a great job on many other parts of SQL, and it's a short and sweet book you could read in a few hours. And it will server as a reference long after you first absorb it.

https://www.oreilly.com/library/view/sql-pocket-guide/978149...

That's the best little book that will teach you the most.