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Since databases are at the center of the IT world, their proper design would seem to be paramount. And yet, some of the popular references on database design theory and design best practice show a curious lack of understanding by the IT industry at large. In this O’Reilly report, C.J. Date—a prominent researcher and consultant specializing in relational database theory—clarifies exactly what database design is, or ought to be. After providing concise definitions of physical and logical database design, Date dives deeper into the subject of logical design. Specifically, he covers concepts such as table predicate, business rule, uncontrolled redundancy, and consistency. Once you digest this report, you can find more detailed information in Date’s book Database Design and Relational Theory: Normal Forms and All That Jazz (O’Reilly, 2012). C.J. Date has a stature that is unique within the database industry. He is a prolific writer, and is well known for his best-selling textbook An Introduction to Database Systems (Addison Wesley).

SQL is full of difficulties and traps for the unwary. You can avoid them if you understand relational theory, but only if you know how to put the theory into practice. In this insightful book, author C.J. Date explains relational theory in depth, and demonstrates through numerous examples and exercises how you can apply it directly to your use of SQL. This second edition includes new material on recursive queries, “missing information” without nulls, new update operators, and topics such as aggregate operators, grouping and ungrouping, and view updating. If you have a modest-to-advanced background in SQL, you’ll learn how to deal with a host of common SQL dilemmas. Why is proper column naming so important? Nulls in your database are causing you to get wrong answers. Why? What can you do about it? Is it possible to write an SQL query to find employees who have never been in the same department for more than six months at a time? SQL supports “quantified comparisons,” but they’re better avoided. Why? How do you avoid them? Constraints are crucially important, but most SQL products don’t support them properly. What can you do to resolve this situation? Database theory and practice have evolved since the relational model was developed more than 40 years ago. SQL and Relational Theory draws on decades of research to present the most up-to-date treatment of SQL available. C.J. Date has a stature that is unique within the database industry. A prolific writer well known for the bestselling textbook An Introduction to Database Systems (Addison-Wesley), he has an exceptionally clear style when writing about complex principles and theory.