1. A method of rewriting a query during a database query processing operation, comprising the steps of: processing the query having one or more target attributes in accordance with at least a portion of a data set producing query results comprising the one or more target attributes and one or more auxiliary attributes, wherein the one or more auxiliary attributes are not included in the query; analyzing the query results with respect to the one or more target attributes and the one or more auxiliary attributes to determine a relative selectivity for the one or more auxiliary attributes; selecting at least one of the one or more auxiliary attributes based at least in part on a ranking of the determined relative selectivity for the one or more auxiliary attributes; and appending the query with at least one new predicate corresponding to the selected at least one of the one or more auxiliary attributes to form a rewritten query; wherein the step of analyzing the one or more target attributes and the one or more auxiliary attributes comprises the steps of: extracting statistics for the one or more auxiliary attributes from the query results; extracting statistics for the one or more auxiliary attributes from the at least a portion of the data set; and evaluating the relative selectivity for the one or more auxiliary attributes in accordance with the statistics from the query results and the statistics from the at least a portion of the data set, wherein the step of evaluating the relative selectivity comprises the step of: comparing a range of the statistics from the query results to a range of the statistics from the at least a portion of the data set for the one or more auxiliary attributes.
7. An article of manufacture for rewriting a query during a database query processing operation; comprising a machine readable storage medium containing one or more programs which when executed implement the steps of claim 1 .