Second normal form (2NF), in database normalization, is a normal form that is met if each attribute that is not part of the primary key depends on all parts of the primary key. More formally, a relation is in the second normal form if it fulfills the following two requirements:
It is in first normal form.
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:
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
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.
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