In simple terms, materialized views are the results of a query that are saved as tables. This means that materialized views do have a physical existence, because they take up disk space in the server.

This article explores the internals of materialized views and demonstrates how to precompute complex aggregates—having Oracle dynamically rewrite SQL to reference precomputed aggregate information.

In Oracle9i, if you specify REFRESH FAST for a single-table aggregate materialized view, you must have created a materialized view log for the underlying table, or the refresh command will fail.