At the safest level, Oracle does not use query rewrite transformations
that rely on unenforced relationships. The valid values for QUERY_REWRITE_INTEGRITY are
ENFORCED (Oracle enforces and guarantees consistency and integrity), TRUSTED (query rewrite
is supported for declared relationships), and STALE_TOLERATED (query rewrite is supported
even if the materialized views are inconsistent with their underlying data). By default, QUERY_
REWRITE_INTEGRITY is set to ENFORCED.
Materialized View Decisions
Before you can create a materialized view, you must make several decisions, including:
Whether the materialized view is to be populated with data during creation or after
How often the materialized view is to be refreshed
What type of refreshes to perform
Whether to maintain a materialized view log or not
You can either have data loaded to the materialized view upon its creation using the build
immediate option of the create materialized view command, or you can add the build deferred
clause to pre-create the materialized view but not populate it until the first time it is used. The
advantage of populating the view on creation is that the data will be available immediately when
you make the materialized view available. However, if the materialized view is not going to be
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614 Oracle Database 11g DBA Handbook
used right away and the underlying data changes rapidly, the data in the materialized view will
become stale rapidly.
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