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The data in a materialized view can be refreshed on demand or incrementally, depending
on the business need. Depending on the complexity of the view??™s underlying SQL statement, the
materialized view can be quickly brought up to date with incremental changes via a materialized
view log.
To create a materialized view, you use the create materialized view command; the syntax for
this command is similar to creating a standard view. Because a materialized view stores the result
of a query, you can also specify storage parameters for the view as if you were creating a table. In
the create materialized view command, you also specify how the view will be refreshed. The
materialized view can be refreshed either on demand or whenever one of the base tables changes.
Also, you can force a materialized view to use materialized view logs for an incremental update,
or you can force a complete rebuild of the materialized view when a refresh occurs.
Materialized views can automatically be used by the optimizer if the optimizer determines that a
particular materialized view already has the results of a query that a user has submitted; the user does
not even have to know that their query is using the materialized view directly instead of the base
tables. However, to use query rewrite, the user must have the QUERY REWRITE system privilege and
you have to set the value of the initialization parameter QUERY_REWRITE_ENABLED to TRUE.
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