5. The apparatus of claim 1 , wherein the operation of comparing the query results to at least the portion of the data set comprises: extracting statistics for the one or more auxiliary attributes from the query results; extracting statistics for the one or more auxiliary attributes from at least the portion of the data set; and evaluating the relative selectivity for the one or more auxiliary attributes by comparing the extracted statistics from the query results to the extracted statistics from at least the portion of the data set.
5. The apparatus of claim 1 , wherein the operation of comparing the query results to at least the portion of the data set comprises: extracting statistics for the one or more auxiliary attributes from the query results; extracting statistics for the one or more auxiliary attributes from at least the portion of the data set; and evaluating the relative selectivity for the one or more auxiliary attributes by comparing the extracted statistics from the query results to the extracted statistics from at least the portion of the data set. 6. The apparatus of claim 5 , wherein the operation of evaluating the relative selectivity comprises: comparing a range of statistics for the one or more auxiliary attributes from the query results to a range of statistics to a corresponding attribute from at least the portion of the data set.