Exploiting maximal redundancy to optimize SQL queries

摘要

Detecting and dealing with redundancy is an ubiquitous problem in query optimization, which manifests itself in many areas of research such as materialized views, multi-query optimization, and query-containment algorithms. In this paper, we focus on the issue of intra-query redundancy, redundancy present within a query. We present a method to detect the maximal redundancy present between a main (outer) query block and a subquery block. We then use the method for query optimization, introducing query plans and a new operator that take full advantage of the redundancy discovered. Our approach can deal with redundancy in a wider spectrum of queries than existing techniques. We show experimental evidence that our approach works under certain conditions, and compares favorably to existing optimization techniques when applicable.