A couple of sites worth checking out to level up, both by Markus Winand:
I ran across https://use-the-index-luke.com organically while learning SWL recently and I've been really enjoying it.
I can't vouch for it from any perspective except as an SQL neophyte but for me it has been teaching me a lot.
also a few different para-sql languages that can be useful, to lower the complexity:
A self para-sql-lang plug if you like the direction of malloy but prefer something closer to native SQL syntax. (a controversial take at times)