1. What is a Database?

• A database is a structured place to store, manage, and retrieve data.
• Web apps use databases for:
  • User accounts (username, password, email).
  • Transactions (shopping cart, orders, payments).
  • Content (posts, comments, logs).
• Databases are accessed via queries → instructions to fetch/update data.

2. SQL Databases

SQL (Structured Query Language) → relational databases that use tables (rows & columns).

Examples:

• MySQL / MariaDB
• PostgreSQL
• Microsoft SQL Server
• Oracle DB

Key Concepts:

• Tables → like spreadsheets (Users, Orders, Products).
• Primary Key → unique ID for each row.
• Foreign Key → links between tables.
• Queries → commands like:
  • SELECT → fetch data
  • INSERT → add data
  • UPDATE → modify data
  • DELETE → remove data

📌 Example query:

SELECT * FROM users WHERE username='alice' AND password='1234';