planet internet rendez vous dating - Updating a materialized view in oracle

Using Views A view is a virtual table consisting of a stored query, it contains no data.A view does not exist, basically its a definition defined within the data dictionary, lots of the DBA_ are views.

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Alternatively, a fast refresh can be performed by transparently detecting when changes to the data in partitions of the base tables occurs and then only the contents of those partitions need be re-computed for refreshing the materialized view.

Similarly, during direct path load operations, such as SQL*Loader direct path loads, the database automatically tracks the new data that is loaded at the block level.

There are two types of refresh modes and 4 types of refresh types.

create materialized view m_dept build immediate refresh fast on commit enable query rewrite as select * from dept; build immediate - populate the materialized view right away refresh fast on commit - use the fast refresh method using the logs create above enable query rewrite - Oracle CBO will rewrite queries to use the new materialized view.

There are a number of reason why we need views statement defining the view is executed, views can be created in your own schema (need CREATE VIEW privilege) or someone else's schema (need CREATE ANY VIEW privilege), you also need privileges on the underlining tables as well.

You also cannot reference any pseudo-columns or expressions when you update a view.

As with view materialized views can be inserted, updated and deleted from.

There are three types of materialized views Query rewrite By setting the parameter QUERY_REWRITE_ENABLED to true (default false) you instruct oracle to automatically update the materialized data with the underlying tables, so if the source data is changed oracle automatically updates the materialized view data.

This is where the CBO comes to play as it now has a choice to use the view to update the table of use the source tables, it calculates the total cost on each taking account for I/O, CPU and memory usage because the materialized has the data already summarized your queries should cost less in resources and hence should run more quicker.

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