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Data & Analytics · Intermediate

Third Normal Form (3NF)

A table is in 3NF when it is in 2NF and no non-key column depends on another non-key column (no transitive dependencies).

Definition

3NF is the standard target for transactional databases. Informally, every non-key attribute must depend on 'the key, the whole key, and nothing but the key'. Transitively dependent attributes are moved to their own tables.

Example

In Employees(EmpID, DeptID, DeptName), DeptName depends on DeptID, so it moves to a Departments table.

Exam tip

Memorize 'the key (1NF), the whole key (2NF), and nothing but the key (3NF)'.

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