Chapter 37. The Rule System

Table of Contents
37.1. The Query Tree
37.2. Views and the Rule System
37.2.1. How SELECT Rules Work
37.2.2. View Rules in Non-SELECT Statements
37.2.3. The Power of Views in PostgreSQL
37.2.4. Updating a View
37.3. Rules on INSERT, UPDATE, and DELETE
37.3.1. How Update Rules Work
37.3.2. Cooperation with Views
37.4. Rules and Privileges
37.5. Rules and Command Status
37.6. Rules Versus Triggers

This chapter discusses the rule system in PostgreSQL. Production rule systems are conceptually simple, but there are many subtle points involved in actually using them.

Some other database systems define active database rules, which are usually stored procedures and triggers. In PostgreSQL, these can be implemented using functions and triggers as well.

The rule system (more precisely speaking, the query rewrite rule system) is totally different from stored procedures and triggers. It modifies queries to take rules into consideration, and then passes the modified query to the query planner for planning and execution. It is very powerful, and can be used for many things such as query language procedures, views, and versions. The theoretical foundations and the power of this rule system are also discussed in On Rules, Procedures, Caching and Views in Database Systems and A Unified Framework for Version Modeling Using Production Rules in a Database System.

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