公开(公告)号：CA2374271A1

公开(公告)日：2003-09-01

申请号：CA2374271

申请日：2002-03-01

Applicant: IBM CANADA

Inventor： KOO FRED ,  LEUNG TING Y

IPC: G06F17/30

Abstract: A query rewrite optimization method for eliminating a redundant join and equivalent subquery in an SQL query before generation and selection of the optimal quer y execution plan. The method evaluates a query for a particular join of a first and second quantifier each ranging over the same table. A determination is made whether the row set produced relative to the second quantifier subsumes the row set produced relative to the first quantifier. The query ma y be reformed to eliminate the join and the second quantifier. A further determination of the removability of the second quantifier may be required such as by evaluating a of a cardinality constraint when query output cardinality is material.