oracle-物化视图

CREATE MATERIALIZED VIEW
http://docs.oracle.com/cd/E11882_01/server.112/e41084/statements_6003.htm#SQLRF01303
When DML changes are made to master table data, Oracle Database stores rows describing those changes in the materialized view log and then uses the materialized view log to refresh materialized views based on the master table. This process is called incremental or fast refresh. Without a materialized view log, Oracle Database must reexecute the materialized view query to refresh the materialized view. This process is called a complete refresh. Usually, a fast refresh takes less time than a complete refresh.

A materialized view log is located in the master database in the same schema as the master table. A master table can have only one materialized view log defined on it. Oracle Database can use this materialized view log to perform fast refreshes for all fast-refreshable materialized views based on the master table.

To fast refresh a materialized join view, you must create a materialized view log for each of the tables referenced by the materialized view.

There are two types of materialized view logs: timestamp-based materialized view logs and commit SCN-based materialized view logs. Timestamp-based materialized view logs use timestamps and require some setup operations when preparing to refresh the materialized view. Commit SCN-based materialized view logs use commit SCN data rather than timestamps, which removes the need for the setup operations and thus can improve the speed of the materialized view refresh. If you specify the COMMIT SCN clause, then a commit SCN-based materialized view log is created. Otherwise, a time-stamp based materialized view log is created.