What are the differences between SQL and NoSQL databases, and when would you choose one over the other?

SQL databases are relational and use structured query language for defining and manipulating data, while NoSQL databases are non-relational and can store unstructured data in various formats (e.g., key-value, document, graph). Choose SQL when data integrity and complex queries are paramount; choose NoSQL for scalability and flexible data models, particularly in applications with high write loads or unstructured data.