Some embodiments provide a non-transitory machine-readable medium stores a program. The program receives a query for data that includes an intersection operation on a first set of strings and a second set of strings. The program further generates a plurality of candidate query execution plans based on the query. The program also determines a plurality of execution costs associated with the plurality of candidate query execution plans. The program further selects a query execution plan from the plurality of candidate query execution plans based on the plurality of execution costs. The program also executes the query execution plan to generate a set of query results for the query.