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

Second Normal Form

The second normalization rule applies only in tables whose primary keys consist of multiple columns. It states that every non-key column must depend on the entire primary key. A table must not contain a non-key column that pertains to only part of a composite primary key. Putting a table into second normal form requires making sure that all the nonprimary key columns (the columns that give information about the subject but do not uniquely define it) relate to the entire primary key and not just to one of its components.

To illustrate, look at the contract column in the titleauthors table (Figure 2.10). Does it apply to each author-title combination? If each author on a book has a separate contract, it does, but if the company ...