Accelerating Queries Based on Exact Knowledge of Specific Rows Satisfying Local Conditions

摘要

A method, computer program product, and system are provided for accelerating a query in a database system. For example, an embodiment of the method may include generating a data structure identifying a set of rows that satisfy conditions local to a table prior to an evaluation of a query and modifying the query based on the data structure. In addition, the method may include repeating the steps with respect to generating the data structure and modifying the query, if one or more additional local conditions are inferred from modifying the query based on the data structure. With respect to the step of modifying the query based on the data structure, in the case where no rows satisfy the local conditions in the data structure, an always false prefilter condition may be migrated as high as possible within the query. When only one row satisfies the local conditions in the data structure, a column may be replaced by a constant value from within that column in that one row. Further, in the case where a moderate number of rows satisfy the local conditions in the data structure and if sensible from a cost basis analysis, an IN condition may be inferred for each column from that table involved in a join condition. Application of these modifications prior to a determination of a query execution plan allows a query to be executed more efficiently and with far lower risk of applying a suboptimal execution plan.