data-design

Data Design

Overview

Principles for designing data structures, schemas, and data flows that are efficient, maintainable, and scalable.

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Data Modeling

Entity-Relationship Diagrams

┌─────────────┐       ┌─────────────┐       ┌─────────────┐
│    User     │       │    Order    │       │   Product   │
├─────────────┤       ├─────────────┤       ├─────────────┤
│ id (PK)     │──┐    │ id (PK)     │    ┌──│ id (PK)     │
│ email       │  │    │ user_id(FK) │←───┘  │ name        │
│ name        │  └───→│ status      │       │ price       │
│ created_at  │       │ total       │       │ stock       │
└─────────────┘       │ created_at  │       └─────────────┘
                      └─────────────┘              │
                             │                     │
                      ┌──────┴──────┐              │
                      ↓             ↓              │
               ┌─────────────┐                     │
               │ OrderItem   │                     │
               ├─────────────┤                     │
               │ id (PK)     │                     │
               │ order_id(FK)│                     │
               │ product_id  │─────────────────────┘
               │ quantity    │
               │ price       │
               └─────────────┘

Relationship Types

Type	Description	Example
1:1	One to one	User ↔ Profile
1:N	One to many	User → Orders
M:N	Many to many	Students ↔ Courses

-- 1:1 (profile extends user)
CREATE TABLE users (
  id SERIAL PRIMARY KEY,
  email VARCHAR(255) UNIQUE
);

CREATE TABLE profiles (
  user_id INTEGER PRIMARY KEY REFERENCES users(id),
  bio TEXT,
  avatar_url VARCHAR(255)
);

-- 1:N (user has many orders)
CREATE TABLE orders (
  id SERIAL PRIMARY KEY,
  user_id INTEGER REFERENCES users(id),
  total DECIMAL(10,2)
);

-- M:N (students ↔ courses via junction table)
CREATE TABLE enrollments (
  student_id INTEGER REFERENCES students(id),
  course_id INTEGER REFERENCES courses(id),
  enrolled_at TIMESTAMP DEFAULT NOW(),
  PRIMARY KEY (student_id, course_id)
);