What is the difference between SQL and NoSQL databases?

**SQL (Relational):** MySQL, PostgreSQL, SQLite
- Structured tables with fixed schema
- ACID compliant (reliable transactions)
- Best for complex queries and relationships
- Example: banking, e-commerce orders

**NoSQL:** MongoDB, Redis, Cassandra
- Flexible schema (documents, key-value, graph)
- Horizontally scalable
- Best for unstructured data and high speed
- Example: user profiles, real-time apps, IoT

Choose SQL for consistency, NoSQL for scalability.