Third normal form

Third Normal Form (3NF)

Definition

A table is in Third Normal Form (3NF) if it is in 2NF and there are no transitive dependencies.

Rules

• 2NF: The table must be in 2NF.
• No Transitive Dependencies: If a table is in 2NF, and a non-key attribute depends on another non-key attribute, then it should be moved to a separate table.

Benefits

• Eliminates Transitive Dependencies: 3NF eliminates transitive dependencies, reducing data redundancy.
• Improves Data Integrity: 3NF ensures that non-key attributes are dependent on the primary key.
• Simplifies Data Maintenance: 3NF makes data maintenance easier by reducing data redundancy.

Example

Consider a table that stores customer information:

Customer ID	Name	Salesperson ID	Salesperson Name
1	John Doe	101	Jane Smith

In this example, Salesperson Name depends on Salesperson ID, which is a transitive dependency. To convert this table to 3NF, we would create separate tables for customers and salespeople:

Customer ID	Name	Salesperson ID
1	John Doe	101

Salesperson ID	Salesperson Name
101	Jane Smith