What is the difference between SQL and NoSQL?

SQL (Structured Query Language) is a query language for working with relational databases, where data is stored in tables with a fixed schema. Main features of SQL databases:

• Strict data schema (table structure is predefined).
• Support for complex JOIN queries.
• Transactions and ACID properties for reliability.

NoSQL is a general term for non-relational databases that can store data in various formats: documents, key-value, graphs, column stores. Main features:

• Flexible or absent schema (schema-less).
• High scalability and performance with large data volumes.
• Support for horizontal scaling.

Examples:

• SQL: PostgreSQL, MySQL
• NoSQL: MongoDB (documents), Redis (key-value), Cassandra (column)

The choice depends on the task: if complex data structure and transactions are important — SQL; if flexibility and scalability are needed — NoSQL.