SQL databases typically use relational tables and relationships. NoSQL is an umbrella term for several data models, including document, key-value, wide-column, and graph databases.

SQL strengths

• Relational modeling and joins.
• Constraints and transaction support.
• Structured querying and reporting.
• Mature indexing and query optimization.

NoSQL models and examples

• Document: MongoDB.
• Key-value: Redis.
• Wide-column: Cassandra.
• Graph: Neo4j.

Choosing a model

• Use SQL when relational integrity, complex queries, and multi-record transactions are central.
• Consider NoSQL when its data model and distribution characteristics match the workload.
• SQL can scale horizontally; NoSQL is not automatically faster.
• Many systems combine relational storage with caches or specialized data stores.