A transformation-based optimizer generates rewritings by applying local algebraic transformation rules on subexpressions of a query. Application of a transformation rule produces substitute expressions, logically equivalent to the original expression. View matching, that is, computing a subexpression from materialized views, is one such transformation rule. The view matching rule applies a view matching technique that determines whether the original query can be computed from one or more of the existing materialized views and, if so, generates substitute expressions. An index structure of materialized views is provided that quickly narrows the search to a set of candidate views on which the view matching techniques can be applied. The index structure, also called a filter tree, speeds up the search for applicable materialized views.