What is the difference between SQL and NoSQL databases?

Answer

SQL (relational) databases store data in tables with fixed schemas and use SQL for queries, offering strong consistency and powerful joins; examples include PostgreSQL, MySQL, and SQL Server. NoSQL databases trade rigid schemas for flexibility and horizontal scale, and come in families such as document (MongoDB), key-value (Redis), wide-column (Cassandra), and graph (Neo4j). Use SQL when you need complex relationships, transactions, and ad-hoc queries; reach for NoSQL when you need schema flexibility, very high write throughput, or scale-out across many nodes. Many systems use both, choosing the right store per workload.