SQL · Quick Reference

Lesson 12 — Database Design & ERDs Cheat Sheet

SQL

In one line: Database normalization serves three core goals:

Key Ideas

1Normalization Goals. Database normalization serves three core goals:

2Entity Relationship Diagrams (ERD). An ERD is a visual blueprint of your database. It shows:

3Relationship Types with Code. The three fundamental relationship types determine where foreign keys go and whether junction tables are needed.

4One-to-One Relationships. A one-to-one relationship stores optional or extension data in a separate table, linked by sharing the same primary key value.

Code Examples

-- One-to-Many: one customer has many orders
CREATE TABLE customers (
  id    INT PRIMARY KEY AUTO_INCREMENT,
  name  VARCHAR(100) NOT NULL,
  email VARCHAR(150) UNIQUE
);

CREATE TABLE orders (
  id          INT PRIMARY KEY AUTO_INCREMENT,
  custo...

-- One user has one profile (optional extension table)
CREATE TABLE user_profiles (
  user_id    INT PRIMARY KEY,   -- same as users.id
  bio        TEXT,
  avatar_url VARCHAR(300),
  FOREIGN KEY (user_id) REFERENCES users(id) ON DELETE CASCADE
);