Specification and optimization of preference (SV-)grouping queries

Preference queries become more and more important in applications like OLAP, data warehousing, or decision support systems. In these environments the Preference SQL GROUPING operation and aggregate functions are extensively used in formulating queries. In this report we present the full specification of the GROUPING operation in Preference SQL. This specification describes the grouping and aggregation known from standard SQL as well as the grouping with substitutable values (SV) semantics to allow a flexible and powerful grouping functionality in comparison to standard SQL. Furthermore, we introduce novel algebraic transformation laws for grouped preference queries and numerical ranking which are one of the most intuitive and practical type of queries. We explain how Preference SQL can be modified to integrate these optimization laws into the existing rule-based query optimizer. Our study upon the well-known TPC-H benchmark dataset shows that significant performance gains can be achieved