Query optimization method for incrementally estimating the cardinality of a derived relation when statistically correlated predicates are applied

摘要

A method, apparatus, and article of manufacture for incrementally estimating the cardinality of a derived relation when statistically correlated predicates are applied. A plurality of query execution plans (QEPs) are generated for the query. During the generation of the QEPs, a cardinality is computed for any of the QEPs in which two or more predicates are correlated to each other. The cardinality comprises a number of rows expected to be returned by the QEP and is computed in an incremental fashion for each operator of the QEP. The computations include calculations that may be done prior to the generation of the QEPs and calculations that are necessarily done as each operator of a QEP is added to that QEP. Thereafter, one of the QEPs is chosen to satisfy the query in a manner that minimizes an estimated cost metric, wherein the cost metric is computed using the cardinality.