🗃️ Lesson 2: Databases & Tables
⏱️ Estimated time: 15 minutes | Difficulty: Beginner
Organizing Information
A database is a collection of related data. Data is organized into tables, which consist of columns (fields) and rows (records).
Creating a Database
CREATE DATABASE my_app;
USE my_app;Creating Tables
CREATE TABLE users (
id INT PRIMARY KEY AUTO_INCREMENT,
name VARCHAR(100) NOT NULL,
email VARCHAR(255) UNIQUE,
age INT,
created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
);Common Data Types
| Type | Description | Example |
|---|---|---|
| INT | Whole numbers | 42 |
| VARCHAR(n) | Text up to n characters | "Hello" |
| TEXT | Long text | Articles, descriptions |
| FLOAT / DOUBLE | Decimal numbers | 3.14 |
| BOOLEAN | True/False | TRUE |
| DATE | Date | '2025-01-15' |
| TIMESTAMP | Date + Time | '2025-01-15 14:30:00' |
Constraints
PRIMARY KEY -- Unique identifier for each row
NOT NULL -- Field cannot be empty
UNIQUE -- No duplicate values
DEFAULT value -- Default value if none given
AUTO_INCREMENT -- Automatically increases (1, 2, 3...)
FOREIGN KEY -- Links to another tableModifying Tables
ALTER TABLE users ADD phone VARCHAR(20);
ALTER TABLE users DROP COLUMN phone;
DROP TABLE users; -- Deletes the whole table!✅ Quick Quiz
❓ What does PRIMARY KEY do?
❓ What data type stores text up to a specific length?
❓ What does NOT NULL mean?