43.4. The PostgreSQL Rule System

PostgreSQL supports a powerful rule system for the specification of views and ambiguous view updates. Originally the PostgreSQL rule system consisted of two implementations:

The query rewriter is discussed in some detail in Chapter 36, so there is no need to cover it here. We will only point out that both the input and the output of the rewriter are query trees, that is, there is no change in the representation or level of semantic detail in the trees. Rewriting can be thought of as a form of macro expansion.