Patent ID: 6826562
Filing Date: 2004-11-30
Classification: G06F,Y10S

Abstract:
A method of optimizing a query in a computer, the query being performed by the computer to retrieve data from database stored in an electronic storage device coupled to the computer, the method comprising the steps of:(a) analyzing the query to determine whether the query includes at least two subselect expressions; (b) if so, determining whether each of the identified subselect expressions returns at most one tuple from the database; (c) if so, performing the subsumption test to determine whether the row sets produced by the two subselect expressions are identical wherein the output columns of the row sets may be different; (d) if so, performing the following steps: (d1) merging the subselect expressions into a single subselect expression, and (d2) merging quantifiers corresponding to said merged subselect expressions and forming a single quantifier; and (e) executing the query in the computer to retrieve data from the database.