What are the best books on relational database modeling in SQL?

Data modeling has little to nothing to do with SQL. What are you trying to accomplish? Designing relational data models?

I suggest Introduction to Database Systems and Database in Depth, both by Chris Date.

I found The Art of PostgreSQL a good resource

https://postgresql.thinkific.com/

SQL Antipatterns is a good one for general design decisions. Use the Index, Luke is a good one for understanding indexes.