Materialized views offer opportunities for significant performance gain in query evaluation by providing fast access to pre-computed data. The question of when and how to use a materialized view in processing a given query is a difficult one attracting a significant amount of research. Whether a materialized view can be used in answering a query depends on the relationship between the view and the query. In previous works only one-to-one or containment mapping from views to a query has been used and, as a result, certain potentially useful materialized views were excluded from consideration. In addition, most of previous works have focused only on conjunctive queries. Proposed in this paper are new ways of utilizing materialized views in answering a query with group-by and aggregation. Views including relations not referred to in an original query, which were excluded in previous works, are utilized. Attributes missing from a view can be recovered under certain conditions. We present ...