Chapter 39. The Rule System

   Table of Contents

   39.1. The Query Tree
   39.2. Views and the Rule System

        39.2.1. How SELECT Rules Work
        39.2.2. View Rules in Non-SELECT Statements
        39.2.3. The Power of Views in PostgreSQL
        39.2.4. Updating a View

   39.3. Materialized Views
   39.4. Rules on INSERT, UPDATE, and DELETE

        39.4.1. How Update Rules Work
        39.4.2. Cooperation with Views

   39.5. Rules and Privileges
   39.6. Rules and Command Status
   39.7. 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 [ston90b] and [ong90].