1.德比：
Derby 是一个用Java实现的功能齐全的开源关系数据库管理系统 (RDBMS)，顾名思义，它是由 Apache Software Foundations 开发的。它基于Java、JDBC 和 SQL 标准。 Derby 易于安装、部署和使用。它要么嵌入到Java应用程序中，要么用作数据库服务器。
2. PostgreSQL :
PostgreSQL 是一个强大的开源对象关系数据库系统。由于其高稳定性，它以低维护工作提供良好的性能。 PostgreSQL 是第一个实现多版本并发控制 (MVCC) 功能的 DBMS。
Derby 和 PostgreSQL 的区别：
| SR.NO. | Derby | PostgreSQL |
|---|---|---|
| 1 | It is developed by Apache Software Foundation in 1997. | It is developed by PostgreSQL Global Development Group in 1989. |
| 2 | It is written in Java language. | It is written in C language. |
| 3 | The primary database model for Derby is Relational DBMS. | The primary database model for PostgreSQL is Relational DBMS. |
| 4 | Server operating systems for Derby are Windows, macOs, Linux, Unix, BSD and z/OS. | PostgreSQL server operating systems are FreeBSD, HP-UX, Linux, NetBSD, OpenBSD, OS X, Solaris, Unix and Windows. |
| 5 | It support only Java programming language. | It supports C, .Net, C++, Java, JavaScript, PHP, Python, Ruby. |
| 6 | APIs and other access methods used by Derby is JDBC. | It uses ADO.NET, JDBC, native C library, ODBC, streaming API for large objects as APIs. |
| 7 | It provide fine grained access rights according to SQL-standard. | It provides access rights for users and roles. |
| 8 | It has Java Stored Procedures for Server-side scripts. | It has user defined functions for Server-side scripts. |
| 9 | It support in-memory capabilities. | It do not support in-memory capabilities. |
| 10 | It supports Secondary indexes. | It also supports Secondary indexes. |