This paper describes the query rewrite facility of the starbust extensible database system, a novel phase of query optimization. we present a suite of rewrite rules used in starbust to transfrom queries into equivalent queries for faster execution, and also describe the production rule engine which is used by starburst to choose and execute these rules. examples are provided demonstrating that these query rewrite transformations lead to query execution time improvements of orders of magnitude, suggesting that query rewrite in general ---- and these rewrite rules in particular --- are an essential step in query optmization for modern database systems.