What are the differences between relational and non-relational databases?

Relational databases (RDBMS) are based on tables with clearly defined schemas and relationships between them. They use SQL for queries and ensure transactional integrity, data consistency, and support for complex joins. Examples: MySQL, PostgreSQL, Oracle.

Non-relational databases (NoSQL) are more flexible, do not require a fixed schema, and can store data as documents, key-value pairs, graphs, or columns. They scale horizontally better and are suitable for large volumes of unstructured data. Examples: MongoDB (documents), Redis (key-value), Cassandra (columnar).

Main differences:

• Schema: Relational — fixed, NoSQL — flexible.
• Data model: Tables vs documents/key-value/graphs.
• Scalability: Relational — vertical, NoSQL — horizontal.
• Transactions: Relational support ACID, NoSQL often sacrifices this for speed and scalability.

The choice depends on data requirements, speed, volume, and structure.