1. A method comprising: identifying a group of two or more predicates from a plurality of predicates in a particular query; generating, based on the group of predicates, a single selectivity value; associating the selectivity value with the group of predicates; and estimating, based on the selectivity value, a cost of executing the particular query, wherein the selectivity of each predicate in the group of predicates is not used to estimate a cost of executing the particular query.