The notes for each day have a list of readings, including papers and readings from two books.

The canonical undergrad textbook is "Database Management Systems" by Ramakrishnan and Gehrke. I've often been confused by papers we read and gone to this book for a foundation before jumping back into the paper. There are a _lot_ of chapters I haven't read (namely the first few on ER diagrams, etc.), but the chapters on storage/indexing/query evaluation/transaction management/normalization are good if you read them a few times.

The graduate-level book is called "The Red Book" (http://redbook.cs.berkeley.edu/), and is a great source of foundational papers in the field. You can find most of the papers online, but the introduction gives you a good sense for the history and evolution of databases.

I hope this helps!