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Data & Analytics · Intermediate

Second Normal Form (2NF)

A table is in 2NF when it is in 1NF and every non-key column depends on the whole primary key, not part of it.

Definition

2NF eliminates partial dependencies, which can only exist when the primary key is composite. Attributes that depend on only one part of the key are moved to their own table.

Example

In OrderLines(OrderID, ProductID, ProductName), ProductName depends only on ProductID, so it moves to Products.

Exam tip

A table with a single-column primary key that is in 1NF is automatically in 2NF.

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