What is PostgreSQL?

PostgreSQL is an object-relational database management system (ORDBMS) based on the POSTGRES, Version 4.2, developed by the University of California, Berkeley computer department. Many of POSTGRES's leading concepts only appear in the business database at very late times.

PostgreSQL is an open source heir to the original Berkeley code. It supports most of the SQL standards and offers many other modern features:

• Complex queries
• FOREIGN key
• Trigger
• View
• Transactional integrity
• Multi-version concurrency control

In addition, PostgreSQL can be extended in a number of ways, such as by adding new:

• Data type
• Function
• Operator
• Aggregation functions
• Index method
• Process language

And, because of the flexibility of the license, anyone can use, modify, and distribute PostgreSQL for free for any purpose, whether private, commercial, or academic research use

For an understanding of foreign keys, see: Http://www.cnblogs.com/ywb-lv/archive/2012/03/12/2391860.html

Trigger:

Basic concepts:

A trigger (trigger) is a special stored procedure whose execution is not invoked by the program or manually, but is triggered by an event, such as when an operation on a table (Insert,delete, update) activates it for execution. Triggers are often used to enforce data integrity constraints, business rules, and so on.　　　　Triggers can be found in the dba_triggers, user_triggers data dictionary.　　Triggers can query other tables and can contain complex SQL statements. Role: Used to enforce complex business rules or requirements, see http://baike.baidu.com/link?url= 1sj8znbjmh2yqncfdvequlmjezqekneitzfmri6og3hlowinxmeyuj-pzm8jih-ntkkf6g3o8wux1j4wpbtxrk

What is PostgreSQL?