Abstract: A query facility for database queries saves and re-uses query execution strategies, and automatically determines whether a strategy can be re-used when an imported variable changes. The query facility automatically saves one or more logical conditions associated with the one or more imported variables in the query. When the query is reused, the logical conditions are evaluated using the imported variable values, and the previously saved execution strategy is used only if the condition or conditions are met. Preferably, the logical conditions express a range of imported variable values which are included in a database subset data structure used by the saved query execution strategy, such as a materialized query table or partitioned table. Logical conditions are preferably generated by negating the predicates from a logical expression defining the applicability of the execution strategy, inserting the negated predicates into the query, and performing a transitive closure.

Abstract: A method and computer program product are provided for implementing skip key processing for database grouping queries involving aggregate operations using one or more indices in a computer system. First checking for a selected entry in a current group in a primary file is performed. Responsive to finding the selected entry in the current group, the set of records of the current group is ordered to provide an aggregate value in an aggregate field of the current group. Then checking for an excluded value in the aggregate field of the current group is performed. Responsive to not finding the excluded value in the aggregate field, a current entry is saved as a result for the group. Then checking for more groups in the primary file is performed. Responsive to finding more groups in the primary file, a unique key or prefix to the query index is obtained to position to a next group. When the selected entry in the next group is not found, then checking for more groups in the primary file is performed.

Abstract: A method and computer program product are provided for processing subquery join composites using hash join in a computer system. A hash table is built for a first table to be joined with a second table. A cursor is built for the second table. For each tuple in the second table, the hash table for the first table is probed. If a match is found, then any non-equal join predicate is evaluated. A unique fanout join is processed to return an error if a tuple or row from the second table joins to more than one row in the first table where the result of the basic predicate subquery can only be one row. A distinct fanout join is processed when the tuple or row from the second table joins to a row in the first table, the row is returned, advancing to a next tuple in the second table without checking for any more matches on the first table.