Tell us about databases: relational and non-relational, that you have worked with.

Relational databases (RDB) are based on tables with clearly defined schemas and relationships between them. They use SQL for queries and are well-suited for structured data with relationships, such as PostgreSQL, MySQL, Oracle. In my experience, I have worked with PostgreSQL — used it for storing user data, transactions, and reports, where integrity and complex queries are important.

Non-relational databases (NoSQL) are more flexible, do not require a fixed schema, and come in different types: document-oriented (MongoDB), key-value (Redis), graph (Neo4j), and columnar (Cassandra). I have used MongoDB for storing JSON-like documents, which is convenient for dynamic data and rapid scaling. Redis was used for caching and session storage.

The choice between them depends on data requirements: if strict structure and transactions are needed — relational; if flexibility and scalability — NoSQL.