How does a relational database differ from a non-relational one?

A relational database (RDB) organizes data into tables with well-defined schemas (rows and columns), where data is linked through keys (such as primary and foreign keys). It uses SQL language for queries and ensures transactional integrity, data consistency, and complex relationships.

A non-relational database (NoSQL) does not require a fixed schema and can store data in various formats: documents (JSON), key-value, graphs, column stores. NoSQL is more flexible and scalable, often used for large volumes of data and distributed systems, but may not guarantee strict transactional integrity.

Example:

• RDB: PostgreSQL, MySQL
• NoSQL: MongoDB (documents), Redis (key-value), Cassandra (columnar)