A materialized view is a view whose result set has been computed and stored on disk, similar to a base table. Conceptually, a materialized view is both a view (it has a query specification stored in the catalog) and a table (it has persistent materialized rows). So, many operations that you perform on tables can be performed on materialized views as well. For example, you can build indexes on, and unload from, materialized views.

Consider using materialized views for frequently executed, expensive queries, such as those involving intensive aggregation and join operations. Materialized views provide a queryable structure in which to store aggregated, joined data. Materialized views are designed to improve performance in environments where the database is large, and where frequent queries result in repetitive aggregation and join operations on large amounts of data. For example, materialized views are ideal for use with data warehousing applications.

Materialized views are precomputed using data from the base tables that they refer to. Materialized views are read-only; no data-altering operations such as INSERT, LOAD, DELETE, and UPDATE can be used on them.

Column statistics are generated and maintained for materialized views in exactly the same manner as for tables. See Optimizer estimates and column statistics.

While you can create indexes on materialized views, you cannot create keys, constraints, triggers, or articles on them.

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