What is the difference between relational and non-relational databases?

Relational databases (RDBs) organize data into tables with well-defined schemas, where data is linked through keys (such as primary and foreign keys). They use SQL language for queries and ensure transactional integrity, data consistency, and complex relationships.

Non-relational databases (NoSQL) do not require a fixed schema and can store data in various formats: documents, key-value, graphs, columns. They are more flexible and scalable, often used for large volumes of data and distributed systems, but may sacrifice strict consistency for performance.

Example differences:

• RDB: a user table with columns id, name, email.
• NoSQL (document database): a collection of documents, where each document is a JSON with an arbitrary structure.