If you are looking for something advanced, you should check books written by C. J. Date. For example, his "An Introduction to Database Systems" considered as one of the best book on database theory.
However he insists on living in his relational purist fantasy land without nulls or outer joins or other pragmatic things that people who use databases to get real work done rely on every day.
However he insists on living in his relational purist fantasy land without nulls or outer joins or other pragmatic things that people who use databases to get real work done rely on every day.