1. PostgreSQL：
PostgreSQL是一个功能强大的开源对象关系数据库系统。它具有较高的稳定性，因此可以在较低的维护工作量下提供良好的性能。 PostgreSQL是第一个实现多版本并发控制(MVCC)功能的DBMS。
2. Amazon SimpleDB：
它是Amazon托管的简单数据库服务，数据存储在Amazon Cloud中。它是Amazon是一项用于实时在结构化数据上运行查询的Web服务。该数据库由Amazon.com用Erlang编写。它具有以下功能–高可用性和灵活性，几乎没有管理负担。
PostgreSQL和Amazon SimpleDB之间的区别：
| S.No. | PostgreSQL | Amazon SimpleDB |
|---|---|---|
| 1. | It is developed By PostgreSQL Global Development Group on 1989. | It is developed By Amazon in 2007. |
| 2. | It is Open Source. | It is commercial. |
| 3. | Server operating systems for PostgreSQL is FreeBSD, HP-UX, Linux, NetBSD, OpenBSD, OS X, Solaris, Unix, Windows. | Server operating systems for Amazon SimpleDB is hosted. |
| 4. | Its Primary database model is a Relational DBMS. | Its primary database model is the Key-value store. |
| 5. | It has predefined data type such as date or float. | It has has no predefined data type such as date or float. |
| 6. | It supports SQL. | It does not support SQL. |
| 7. | APIs and other access methods for PostgreSQL is ADO.NET, JDBC, native C library, ODBC, streaming API for large objects. | APIs and other access methods for Amazon SimpleDB is RESTful HTTP API. |
| 8. | Programming languages supported by PostgreSQL are .Net, C, C++, Delphi, Java, JavaScript (Node.js), Perl, PHP, Python, Tcl. | Programming languages supported by Amazon SimpleDB are .Net, C, C++, Erlang, Java, PHP, Python, Ruby, Scala. |
| 9. | It supports Server-side scripting using user defined functions. | It does not support Server-side scripting. |
| 10. | It supports Triggers. | It does not support Triggers. |
| 11. | It supports Partitioning methods using partitioning by range, list and (since PostgreSQL 11) by hash. | It does not support Partitioning methods. |
| 12. | It provides the concept of Referential Integrity. Hence, there is Foreign Keys. | It does not provide the concept of Referential Integrity. Hence, there is no Foreign Keys. |
| 13. | It supports ACID properties. | It does not support ACID properties. |