I highly recommend "How Query Engines Work" by Andy Grove (author of the Apache Datafusion Query Engine + Apache Ballista Distributed scheduler)

It's written in Kotlin and is very intelligible + succinct (99 pages):

https://leanpub.com/how-query-engines-work

https://github.com/andygrove/how-query-engines-work

As a self-assessment, I rewrote the entire implementation from a columnar/vector-based engine (it uses Arrow) to row-based, using JDBC types, and it took me only 2 readthroughs of the book to be able to do that.

There's also "Database Design and Implementation" by Edward Sciore

Look through https://www.reddit.com/r/databasedevelopment, including posts like this: https://www.reddit.com/r/databasedevelopment/comments/u7v693....