First Normal Form (1NF)

Goal:

• Eliminate repeating groups.
• Make sure each field contains atomic (indivisible) values.

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A table NOT in 1NF:

student_id	name	courses
1	Alice	Math, History
2	Bob	Math

Problem:

• courses has multiple values in one column — this is not atomic.

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Fix — Table in 1NF:

Break it into one row per course:

student_id	name	course
1	Alice	Math
1	Alice	History
2	Bob	Math

✅ Each field contains atomic values.
✅ No multi-valued columns.

Second Normal Form (2NF)

Goal:

• Be in 1NF AND
• Eliminate partial dependencies (no attribute should depend only on part of a composite primary key).

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A table in 1NF but NOT in 2NF:

Assume the primary key is (student_id, course).

student_id	course	student_name
1	Math	Alice
1	History	Alice
2	Math	Bob

Problem:

• student_name depends only on student_id, not on the whole key (student_id, course).
• This is a partial dependency.

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Fix — Table in 2NF:

Split into two tables:

Students

student_id	student_name
1	Alice
2	Bob

Enrollments

student_id	course
1	Math
1	History
2	Math

✅ Now every non-key column depends on the whole primary key.

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).

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.