1. 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。
2.IBM Db2：
IBM Db2 是由 IBM 开发的一系列数据管理产品，包括数据库服务器。它是一个关系数据库管理系统 (RDBMS)，支持面向对象的特性和非关系结构的 XML。 Db2 旨在高效地存储、分析和检索数据。它最初于 1983 年发布，使用 C、C++、 Java和汇编语言编写。
PostgreSQL 和 IBM Db2 的区别：
| SR.NO | PostgreSQL | IBM Db2 |
|---|---|---|
| 1. | It is developed by PostgreSQL Global Development Group in 1989. | It is developed by IBM in 1983. |
| 2 | PostgreSQL server operating systems are FreeBSD, HP-UX, Linux, NetBSD, OpenBSD, OS X, Solaris, Unix and Windows. | Db2 server operating systems are AIX, HP-UX, Linux, Solaris, Windows and z/OS. |
| 3 | The primary database model for PostgreSQL is Relational DBMS. | The primary database model for IBM Db2 is Relational DBMS. |
| 4 | It is written in C language. | It is written in C, C++, Assembly language, Java languages. |
| 5 | Famous companies like National Audubon Society, Inc., FreshRealm, LLC, TIME Systems etc uses PostgreSQL. | Famous companies like JPMorgan Chase, Bank of America, Scotiabank, Citi, etc use Db2. |
| 6 | It uses ADO.NET, JDBC, native C library, ODBC, streaming API for large objects as APIs. | It uses ADO.NET, JDBC, JSON style queries info, ODBC, XQuery as APIs . |
| 7 | It is a open source software framework. | It is a commercial databases. |
| 8 | It supports Secondary indexes. | It supports the secondary indexes without any restrictions. |
| 9 | It supports C, .Net, C++, Java, JavaScript, PHP, Python, Ruby. | It supports C, C++, Cobol, Java, Perl, PL/1, Python, R, Ruby. |
| 10 | It provides access rights for users and roles. | It provide fine grained access rights according to SQL-standard. |