Normalization organizes data to reduce redundancy and improve integrity. The three main normal forms (1NF, 2NF, 3NF) progressively eliminate different types of data anomalies.

First Normal Form (1NF)

Rule: Each cell contains a single value, no repeating groups.

Before 1NF (Bad)

| customer_id | name  | phones              |
|-------------|-------|---------------------|
| 1           | Alice | 555-0001, 555-0002  |

After 1NF (Good)

| customer_id | name  | phone    |
|-------------|-------|----------|
| 1           | Alice | 555-0001 |
| 1           | Alice | 555-0002 |

Second Normal Form (2NF)

Rule: Must be in 1NF, and no partial dependencies (all non-key columns depend on the entire primary key).

Before 2NF (Bad)

-- Primary key is (order_id, product_id)
| order_id | product_id | customer_name | product_name |
|----------|------------|---------------|--------------|
| 1        | 101        | Alice         | Widget       |
-- customer_name depends only on order_id, not full key!

After 2NF (Good)

-- Orders table
| order_id | customer_name |
|----------|---------------|
| 1        | Alice         |

-- Order_items table
| order_id | product_id | product_name |
|----------|------------|--------------|
| 1        | 101        | Widget       |

Third Normal Form (3NF)

Rule: Must be in 2NF, and no transitive dependencies (non-key columns can't depend on other non-key columns).

Before 3NF (Bad)

| employee_id | name  | dept_id | dept_name    |
|-------------|-------|---------|--------------|
| 1           | Alice | 10      | Engineering  |
-- dept_name depends on dept_id, not employee_id!

After 3NF (Good)

-- Employees table
| employee_id | name  | dept_id |
|-------------|-------|---------|
| 1           | Alice | 10      |

-- Departments table
| dept_id | dept_name    |
|---------|--------------|
| 10      | Engineering  |

Benefits of Normalization

• Eliminates data redundancy
• Prevents update anomalies
• Improves data consistency
• Makes database structure clearer