Predicate Derivation and Monotonicity Detection in DB2 UDB

DB2 Universal Database allows database schema designers to specify generated columns. These generated columns are useful for maintaining rollup hierarchy variables in warehouses (e.g., date, month, quarter). In order for the generated columns to be useful for query processing, queries must automatically make use of such columns when applicable. In particular, query predicates on the original columns should be rewritten to make use of the generated columns. In this paper, we describe two main aspects of this predicate rewriting technique that allows usage of the generated columns for a variety of query predicate types. The first aspect, monotonicity detection, allows for rewrites in the case of range predicates. The second aspect, predicate derivation, is the technique for using generating expressions for query processing. We show the value of this technique for providing significant performance improvement when combined with indexing or multidimensional clustering in DB2.