The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Sep. 08, 2009
Filed:
Feb. 27, 2003
Fred Koo, Thornhill, CA;
Ting Y. Leung, San Jose, CA (US);
Fred Koo, Thornhill, CA;
Ting Y. Leung, San Jose, CA (US);
International Business Machines Corporation, Armonk, NY (US);
Abstract
A method, computer readable medium, and system for optimizing a query in a relational database processing system is disclosed. The present invention relates to a query rewrite optimization method for eliminating a redundant join and equivalent subquery in an SQL query before generation and selection of the optimal query execution plan. The method of the present invention includes evaluating the query to identify a join predicate joining a sub-expression of the query to itself, and determining whether a row set producible from a first set of references of the query to the sub-expression is subsumed by a row set producible from a second set of references of the query to the sub-expression. Based on such evaluation and determination, the query may be reformed to eliminate the join predicate and the second quantifier. A further determination of the removability of the second quantifier may be required such as by evaluating a cardinality constraint when query output cardinality is material.