SYSTEM AND METHOD FOR OPTIMIZING DATABASE QUERIES

摘要

A system and method for optimizing a database query with improved performance enhancements. The database query (148) consists of one or more logical expressions. Through the repeated application of one or more rules, the logical expressions are transformed into execution plans (150). The query optimizer (120) partitions the database query (148) into one or more subproblems with each subproblem consisting of one or more logical expressions. A plan is obtained for each subproblem included in the plan (150) for the query (148). The query optimizer (120) is cost-based and uses rules including transformation and implementation rules to perform transformations on the logical expressions in a subproblem which produces a plan (150). The rules are classified into context-free and context-sensitive in order to avoid generating duplicate expressions. Context-free rules are applied once for each logical expression and context-sensitive rules are applied once for each logical expression for a particular optimization goal.