What database management systems are you familiar with and have used in projects?

Database management systems (DBMS) come in different types, and projects often use:

• Relational DBMS (SQL): MySQL, PostgreSQL, Microsoft SQL Server, Oracle Database. Used for structured data with clear relationships.
• Document-oriented DBMS (NoSQL): MongoDB, CouchDB. Good for flexible schemas and storing JSON-like documents.
• Key-value: Redis, Memcached. Used for caching and fast data access.
• Columnar DBMS: Apache Cassandra, HBase. Suitable for analytics on large volumes of data.

In testing, I often interacted with MySQL and MongoDB, verifying query correctness, data integrity, and performance.