Third Normal Form

Third Normal Form (3NF) in database normalization aims to remove transitive dependencies within tables. It ensures that each non-primary key attribute is dependent only on the primary key and not on other non-primary key attributes. Achieving 3NF involves breaking down tables to eliminate such dependencies.

For instance, consider a table named "Employee_Details" with columns: Employee_ID (Primary Key), Employee_Name, Department_ID, and Department_Name.

The objective of the Third Normal Form (3NF) is to eliminate transitive dependencies within a table. Let's illustrate the transformation of a table into 3NF by resolving such dependencies.

Consider a table named "Employee_Info" storing employee details such as Employee ID, Employee Name, Department ID, and Department Name.

Original Table: Employee_Info


Transformation into 3NF:

Identifying Transitive Dependency:

The Department Name attribute depends not only on the Employee ID but also on the Department ID, creating a transitive dependency.

Decomposition into 3NF:

Employee Information Table (3NF):


Department Table (3NF):

Result (3NF):

  • The Employee Information Table contains unique employee details without transitive dependencies.
  • The Department Table separates the Department ID and Department Name, ensuring each table represents distinct information and adheres to the Third Normal Form (3NF).

Additionally, let's consider further examples of tables in Third Normal Form (3NF) - "STUDENT," "COURSE," "PROFESSOR," and their mapping through "STUDENT_COURSE."

Additional Examples on Third Normal Form (3NF):

STUDENT Table (3NF):

COURSE Table (3NF):

PROFESSOR Table (3NF):


STUDENT_COURSE Table (3NF):


Each of these tables STUDENT, COURSE, PROFESSOR, and the mapping table STUDENT_COURSE is structured independently, ensuring no transitive dependencies exist within any single table, thereby adhering to the Third Normal Form (3NF).

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