Apparatus, method, and computer program product for processing query

摘要

A plan combining unit combines a plan including all predicate nodes by increasing a size of a subplan stepwise while selecting the subplan with a low cost using an analysis graph generated by a query analyzing unit and plan combination constraint data extracted by a constraint extracting unit. The analysis graph is the one expressed by a graph including a variable node corresponding to a variable to which an object on a database is bound and a predicate node indicating a condition between the variable nodes. The plan combination constraint data represents a constraint to a plan and a subplan extracted from the analysis graph as a condition between the nodes.