Third Normal Form (3NF)

Goal:

• Be in 2NF AND
• Eliminate transitive dependencies (non-key columns must depend only on the primary key, not on other non-key columns).

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A table in 2NF but NOT in 3NF:

student_id	student_name	student_zipcode	zipcode_city
1	Alice	12345	New York
2	Bob	67890	Los Angeles

Problem:

• zipcode_city depends on student_zipcode, not directly on student_id.
• This is a transitive dependency: student_id → student_zipcode → zipcode_city.

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Fix — Table in 3NF:

Split into two tables:

Students

student_id	student_name	student_zipcode
1	Alice	12345
2	Bob	67890

Zipcodes

student_zipcode	zipcode_city
12345	New York
67890	Los Angeles

✅ Now, all non-key columns depend only on the primary key.

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Summary Table

Normal Form	What It Fixes	Requirement
1NF	Repeating groups, multivalued columns	Atomic values (no lists or sets inside fields).
2NF	Partial dependencies	No non-key column depends on part of a composite key.
3NF	Transitive dependencies	No non-key column depends on another non-key column.

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🎯 In Simple Words:

• 1NF: One value per cell.
• 2NF: No partial key dependency.
• 3NF: No indirect dependency.