1. A method of optimizing execution of a query that accesses data stored on a data store connected to a computer, comprising: generating cardinality estimates for one or more query execution plans for the query using statistics of one or more automatic summary tables that vertically overlap the query, wherein the statistics of the one or more automatic summary tables are used to improve a combined selectivity estimate of one or more predicates of the query, wherein the predicates are applied by one of the automatic summary tables, and wherein the selectivity estimate comprises a ratio of a cardinality of the automatic summary table to a product of cardinalities of base tables referenced in the automatic summary table and the query; using the generated cardinality estimates to determine an optimal query execution plan for the query; and executing the optimal query execution plan for the query in order to access the data stored on the data store connected to a computer and then output the accessed data.