Apache Derby
Apache Derby is an open-source, lightweight relational database management system (RDBMS) implemented entirely in Java. It is designed to be embedded in Java applications, requiring minimal administration and offering a small footprint, making it ideal for single-user or small-scale deployments. Derby supports standard SQL and JDBC, providing ACID transactions and a full-featured database engine that can run in embedded mode or as a network server.
Developers should learn Apache Derby when building Java applications that require a lightweight, embeddable database for prototyping, testing, or small-scale production use, such as desktop applications, mobile apps, or development environments. It is particularly useful in scenarios where minimal setup and zero administration are priorities, as it eliminates the need for a separate database server installation. Derby is also valuable for educational purposes or in embedded systems where resource constraints are a concern.