METHOD, COMPUTER PROGRAM PRODUCT, AND SYSTEM FOR REWRITING DATABASE QUERIES IN A HETEROGENEOUS ENVIRONMENT

A method, computer product, and system for rewriting database without decreasing pushdownability is provided. First, a pushdown analysis of the query in its entirety is performed prior to the application of any query rewrite rules in order to establish a baseline on pushdownability for the query. The results of this analysis is stored with the internal query representation. After each rule is applied to rewrite a portion of a query, that rewritten portion is analyzed again for pushdownability. If pushdownability is not decreased, then the rewritten query remains and the internal representation of the query is updated to reflect the pushdownability of that portion. If pushdownability is decreased, then an undo operation is applied to the rewritten portion of the query to back out the effects of the rule and leave the query in the same state as before the rewrite. Finally, additional rewrite rules that are directed to the heterogeneous database environment are also provided.