Back 1000 years ago when I took my first (and my University’s first) relational database class, the book we used was by Mr. Date. I still have a copy of that book and refer to it now and then. If you'd like to hear from one of the founders of relational database systems here is your opportunity.
He spoke at the Hotsos symposium a few years back and I found the talk to be quite informative.
SQL and Relational Theory: How to Write Accurate SQL
-- A Chris Date Master Class
Chris Date is coming to Cleveland October 22nd-24th to present the course: “SQL and Relational Theory: How to Write Accurate SQL”. For less than $600 spend 3 days with CJ Date to see how to solve your problems with relationally accurate techniques. Don't miss this opportunity learn from one of the founders of relational theory. Invest in yourself to fine tune skills you will need for the rest of your professional life. Course details: https://www.neooug.org/DateSeminar/ChrisDate_SQL_and_relational_theory.htm