A view takes the output of a query and makes it appear like a virtual table. You can use a view in most places where a table can be used.All operations performed on a view will affect data in the base table and so are subject to the integrity constraints and triggers of the base table.
A View can be used to simplify SQL statements for the user or to isolate an application from any future change to the base table definition.
A View can also be used to improve security by restricting access to a predetermined set of rows or columns.In addition to operating on base tables, one View can be based on another, a view can also JOIN a view with a table (GROUP BY or UNION).
Materialized views are schema objects that can be used to summarize, precompute, replicate, and distribute data. E.g. to construct a data warehouse.
A materialized view provides indirect access to table data by storing the results of a query in a separate schema object. Unlike an ordinary view, which does not take up any storage space or contain any data.The existence of a materialized view is transparent to SQL, but when used for query rewrites will improve the performance of SQL execution. An updatable materialized view lets you insert, update, and delete.
You can define a materialized view on a base table, partitioned table or view and you can define indexes on a materialized view.A materialized view can be stored in the same database as its base table(s) or in a different database.
Materialized views stored in the same database as their base tables can improve query performance through query rewrites. Query rewrites are particularly useful in a data warehouse environment.
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