Oracle Physical Design Forms

First Normal Form
In essence, a relation is in first normal form if it does not contain any repeating values. Here, we have taken our relations with repeating values and moved them to separate relations. When the new relations are created, we carry the primary key of the original relation into the new relation.

Second Normal Form

The purpose of the second normal form (2NF) test is to check for partial key dependencies. Partial key dependencies are created when we break off an unnormalized relation into first normal form by carrying the key, thereby creating a concatenated key with several data items. The formal definition of second normal form is as follows:

A relation is in second normal form if and only if the relation is in first normal form and each no-key attribute is fully functionally dependent on the entire concatenated key.

However, I prefer the following definition:

A relation is in second normal form if each attribute depends on the key, the whole key, and nothing but the key, so help me Codd.

It should be apparent that the second normal form test only applies to relations that have more than one key field. A relation in first normal form that only has one key is automatically in second normal form if each attribute is functionally dependent on the key.

This is an excerpt from "High Performance Data Warehousing", copyright 1997.

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