What databases have you worked with? Relational, non-relational?

In work, I had to use both relational and non-relational databases.

Relational databases:

• PostgreSQL — for storing structured data with support for complex queries and transactions.
• MySQL — for projects with a classic relational model.

Non-relational databases:

• MongoDB — for storing documents in JSON format, where the data structure can be flexible.
• Redis — as an in-memory store for caching and quick data access.
• Cassandra — for distributed storage of large volumes of data with high availability.

The choice of database depends on the project requirements: need for transactions, scalability, data structure, and access speed.