2.4. Third Normal Form (3NF)
Another normal form can address these problems. A table is in Third Normal Form (3NF) if for all X → Y, where X and Y are columns of a table, X is a key or Y is part of a candidate key. (A candidate key is a unique set of columns that identify each row in a table; you cannot remove a column from the candidate key without destroying its uniqueness.) This implies that the table is in 2NF, since a partial key dependency is a type of transitive dependency. Informally, all the nonkey columns are determined by the key, the whole key, and nothing but the key.
The usual way that 3NF is explained is that there are no transitive dependencies. A transitive dependency is a situation where we have a table with columns (A, B, ...
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