Practical SQL Handbook, The: Using SQL Variants, Fourth Edition

Third Normal Form

Third normal form applies the principle addressed by second normal form in a more general way: It's not limited to composite primary keys. Third normal form requires that no non-key column depend on another non-key column. Each non-key column must be a fact about the primary key column.

In the authors table, the primary key is au_id. When you check each column, you find that au_ord (the position of an author's name on a multiauthor book) is not about an individual author (au_id) because an author might have several books and might occupy a different position on each (first, second, or third author). Author order really concerns each author-title relationship. The same is true of royaltyper. Both of these columns belong in the ...