These are the books I recommend you read if you want to learn more about database design or expand your knowledge of SQL. Keep in mind that some of these books will be challenging because they are more technical in nature. Also, some authors assume that you have a fairly significant background in computers, databases, and programming.
Connolly, Thomas, and Carolyn Begg. Database Systems: A Practical Approach to Design, Implementation, and Management (6th ed.). Essex, England: Addison-Wesley, 2014.
Coronel, Carlos and Steven Morris. Database Systems: Design, Implementation, and Management (11th ed.). Stamford, CT: Cengage Learning, 2015.
Date, C.J. An Introduction to Database Systems (8th ed.). Boston, MA: Addison-Wesley, 2003.
Date, C.J. Database in Depth: Relational Theory for Practitioners. Sebastopol, CA: O’Reilly Media, 2005.
Date, C.J. Database Design and Relational Theory: Normal Forms and All That Jazz. Sebastopol, CA: O’Reilly Media, 2012.
Hernandez, Michael J. Database Design for Mere Mortals (3rd ed.). Boston, MA: Addison-Wesley, 2013.
Bowman, Judith S., Sandra L. Emerson, and Marcy Darnovsky. The Practical SQL Handbook: Using SQL Variants (4th ed.). Boston, MA: Addison-Wesley, 2001.
Celko, Joe. Joe Celko’s SQL for Smarties: Advanced SQL Programming (5th ed.). Burlington, MA: Morgan Kaufmann Publishers, 2014.
Date, C.J., and Hugh Darwen. A Guide to the SQL Standard (4th ed.). Reading, MA: Addison-Wesley, 1996.
Rockoff, Larry. The Language of SQL (2nd ed.). Boston, MA: Addison-Wesley, 2016.
Viescas, John L., Douglas J. Steele, and Ben G. Clothier. Effective SQL: 61 Ways to Write Better SQL. Boston, MA: Addison-Wesley, 2016.