Designing views to efficiently answer real SQL queries

Abstract

The problem of optimizing queries in the presence of materialized views and the related view-design problem have recently attracted a lot of attention. Significant research results have been reported, and materialized views are increasingly used in query evaluation in commercial data-management systems. At the same time, most results in the literature assume set-theoretic semantics, whereas SQL queries have bagtheoretic semantics (duplicates are not eliminated unless explicitly requested). This paper presents results on selecting views to answer queries in relational databases under set, bag, and bag-set semantics. The results can be used under each of the three assumptions, to find sound and complete algorithms for designing views and rewriting queries efficiently.