SQL · Quick Reference

Lesson 13 — Normalization 1NF 2NF 3NF Cheat Sheet

SQL

In one line: Without normalization you get three types of anomalies:

Key Ideas

1Why Normalize?. Without normalization you get three types of anomalies:

21NF — First Normal Form. Rule: Every column must contain atomic (single, indivisible) values. No repeating groups or sets of values in one cell.

32NF — Second Normal Form. Rule: Must be in 1NF and have no partial dependencies. Every non-key column must depend on the entire primary key — not just part of it. This only matters when the PK ...

43NF — Third Normal Form. Rule: Must be in 2NF and have no transitive dependencies. A non-key column must not depend on another non-key column.

5When to Denormalize. Normalization is great for OLTP (Online Transaction Processing) systems — apps that INSERT, UPDATE, DELETE frequently. However, OLAP (Online Analytical Processing) sys...

Code Examples

-- VIOLATES 1NF: courses column stores multiple values
-- student_id | name  | courses
-- 1          | Sara  | Math, Science, English

-- CORRECT 1NF: separate rows per course
-- student_id | name  | course
-- 1          | Sara  | Math
-- 1          ...

-- VIOLATES 2NF: student_name depends only on student_id, not course_id
-- (student_id, course_id) → student_name, course_name, grade
-- student_name depends on PART of the composite key

-- FIX: decompose into three tables
-- students(id, student_name...

-- VIOLATES 3NF: zip_code determines city (transitive dependency)
-- order_id → customer_zip → customer_city
-- customer_city depends on zip_code, not order_id

-- FIX: extract zip codes into their own table
-- orders: order_id, customer_id, zip_code
...