1NF, 2NF, 3NF: Database Normalization Levels Every SQL Developer Must Know

What Is 1NF, 2NF, and 3NF?

1NF (First Normal Form) requires atomic columns, unique rows, and no repeating groups, ensuring each cell holds a single value.

2NF (Second Normal Form) builds on 1NF by removing partial dependency—every non-key column must depend on the whole composite key, eliminating redundant data across composite keys.

3NF (Third Normal Form) extends 2NF by eliminating transitive dependency—non-key columns depend only on the primary key, not on other non-key columns.

Why Does Normalization to 3NF Matter?

Normalization minimizes update, insert, and delete anomalies, making data maintenance predictable and less error-prone.

Well-normalized schemas reduce storage costs and improve query accuracy by eliminating duplicate or inconsistent data.

How Do I Check If a Table Is in 1NF?

Verify that each column is atomic and contains a single data type; remove any repeating groups or arrays into separate tables.

How Do I Bring a Table to 2NF?

Identify composite primary keys, move attributes that depend only on part of the key into new tables, and reference them via foreign keys.

What Steps Convert 2NF Tables to 3NF?

Find non-key columns that depend on other non-key columns, place them in separate tables, and keep only the primary key as a foreign key back to the original table.

Real-World Example: Orders Schema Before & After Normalization

Before: ORDER(order_id, customer_name, customer_city, product_name, product_price)

CREATE TABLE orders_raw (
order_id INT PRIMARY KEY,
customer_name TEXT,
customer_city TEXT,
product_name TEXT,
product_price NUMERIC
);

After 3NF: CUSTOMER(customer_id, name, city); PRODUCT(product_id, name, price); ORDER(order_id, customer_id, product_id)

CREATE TABLE customers (
customer_id INT PRIMARY KEY,
name TEXT,
city TEXT
);
CREATE TABLE products (
product_id INT PRIMARY KEY,
name TEXT,
price NUMERIC
);
CREATE TABLE orders (
order_id INT PRIMARY KEY,
customer_id INT REFERENCES customers(customer_id),
product_id INT REFERENCES products(product_id)
);

Best Practices for Maintaining 3NF

Establish clear naming conventions, always design with primary and foreign keys, and use SQL constraints to enforce referential integrity.

Automate schema reviews via migration scripts and code reviews to catch new transitive dependencies early.

How Can Galaxy Help With Normalization?

Galaxy’s AI copilot reviews CREATE TABLE statements, highlights partial or transitive dependencies, and suggests refactors to reach 3NF.

Galaxy Collections let teams endorse normalized schemas, ensuring everyone reuses trusted table definitions rather than ad-hoc ones.

Code Snippet: AI-Assisted Refactor in Galaxy

-- Prompt to Galaxy AI
/* Refactor this table to 3NF */
CREATE TABLE employee_raw (
emp_id INT PRIMARY KEY,
emp_name TEXT,
dept_name TEXT,
dept_head TEXT
);


When Might You Skip Full 3NF?

For read-heavy analytics or star schemas, slight denormalization can improve performance; document the trade-off and monitor data quality.

Key Takeaways

1NF removes repeating groups, 2NF removes partial dependency, 3NF removes transitive dependency.Together they ensure reliable, maintainable data.

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