PostgreSQL is implemented using a simple "process per user" client/server model. In this model there is one

Here we give a short overview of the stages a query has to pass in order to obtain a result.

The parser stage consists of two parts: The parser defined in gram

The task of the planner/optimizer is to create an optimal execution plan. A given SQL query (and hence, a query tree) can be actually executed in a

The executor takes the plan created by the planner/optimizer and recursively processes it to extract the required set of rows. This is essentially

The examples shown below use tables in the PostgreSQL regression test database. The outputs shown are taken from version 8.3. The behavior

PostgreSQL supports a powerful rule system for the specification of views and ambiguous