What databases have you worked with? What types of databases do you know? Why are relational databases called relational?

I have worked with relational databases such as PostgreSQL and MySQL, as well as with non-relational ones like MongoDB and Redis.

Types of databases:

• Relational (SQL): data is stored in tables with clearly defined relationships between them.
• Document-oriented (NoSQL): data is stored as documents, for example JSON.
• Key-value: a simple structure where data is stored by key.
• Column-oriented: optimized for analytics, storing data by columns.
• Graph: store data in the form of graphs, suitable for complex relationships.

Relational databases are called so because data is organized in the form of relations (tables), where each table represents a set of tuples (rows), and relationships between tables are expressed through keys. This is based on the relational data model proposed by Edgar F. Codd.