This book is a textbook for a first graduate or advanced undergraduate computer science course on database systems. The author's decades of experience with a database vendor, with an organization that develops database applications and teaching graduate database courses have provided unique insights into the knowledge that's needed for success in applications development, as well as what students don't learn in typical courses. This book emphasizes those areas that are most needed for success in application development, and the areas that are typically not covered well. The approach uses avoids superfluous mathematics that's not needed to understand the concepts, so that time is not wasted on proofs that are of no practical value to the student.