Second normal form

This article includes a list of general references, but it lacks sufficient corresponding inline citations. Please help to improve this article by introducing more precise citations. (June 2024) (Learn how and when to remove this message)

Second normal form (2NF), in database normalization, is a normal form. A relation is in the second normal form if it fulfills the following two requirements:

1. It is in first normal form.
2. It does not have any non-prime attribute that is functionally dependent on any proper subset of any candidate key of the relation (i.e. it lacks partial dependencies). A non-prime attribute of a relation is an attribute that is not a part of any candidate key of the relation.

Put simply, a relation (or table) is in 2NF if:

1. It is in 1NF and has a single attribute unique identifier (UID)(in which case every non key attribute is dependent on the entire UID), or
2. It is in 1NF and has a multi-attribute unique identifier, and every regular attribute (not part of the UID) is dependent on all attributes in the multi-attribute UID, not just one attribute (or part) of the UID.

If any regular (non-prime) attributes are predictable (dependent) on another (non-prime) attribute, that is addressed in third normal form.