Notes

SQL

Published on October 25, 2025

Chapter 1 — Database Basics

What is a Database?

A database is a structured system to store, manage, and retrieve data efficiently.

SQL (Relational Databases)

Data stored in tables (rows & columns)
Fixed schema
Uses SQL
Strong data integrity and relationships
Best for structured data

Examples:

PostgreSQL
MySQL
SQLite

NoSQL (Non-Relational Databases)

Flexible data formats (JSON, key-value, graph)
No fixed schema
Designed for scalability and speed
Can cause data duplication

Examples: