The SQLite Query Optimizer Overview

The SQLite Query Planner

This document provides overview of how the query planner and optimizer for SQLite works.

Given a single SQL statement, there might be dozens, hundreds, or even thousands of ways to implement that statement, depending on the complexity of the statement itself and of the underlying database schema. The task of the query planner is to select an algorithm from among the many choices that provides the answer with a minimum of disk I/O and CPU overhead.

Additional background information is available in the indexing tutorial document.

With release 3.8.0, the SQLite query planner was reimplemented as the Next Generation Query Planner or "NGQP". All of the features, techniques, and algorithms described in this document are applicable to both the pre-3.8.0 legacy query planner and to the NGQP. For further information on