What is the difference between SQL and NoSQL databases and when to use each with Node.js?
Answer
SQL databases (PostgreSQL, MySQL, SQLite) use structured tables with a fixed schema, enforce ACID transactions, and use SQL for querying. They excel at complex queries with joins, strict data integrity, and well-defined relational data. Use SQL for: financial data, e-commerce (orders, inventory), applications needing complex reporting, or when data relationships are complex and well-understood. Node.js drivers: pg (PostgreSQL), mysql2, with ORMs like Prisma, Sequelize, TypeORM. NoSQL databases (MongoDB, Redis, Cassandra, DynamoDB) offer flexible schemas, horizontal scaling, and specific optimizations for particular data patterns. Use NoSQL for: document stores (MongoDB for content, user profiles, catalogs), key-value cache (Redis), real-time analytics (Cassandra for time-series), or when schema evolves rapidly. Node.js drivers: mongoose (MongoDB), ioredis (Redis). In practice, many applications use both — PostgreSQL for transactional data and Redis for caching and sessions.