Oracle Corporation
HASH BASED SET OPERATIONS

Abstract:

Computer-implemented techniques for hash-based set operations. In some embodiments, the techniques are implemented in a computer database management system to improve the computational space or time efficiency of executing database query language statements that contain one or more set operations. With the hash-based techniques, duplicate record elimination and aggregation of the component query result sets is not required before combining the sets in a set operation as the set operation itself performs aggregation on the records. As a result, the computational efficiency of performing the set operation is improved over a sort-based approach where a component query result set is not pre-sorted.