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Unknown April 24, at AM. Unknown January 3, at AM. Unknown September 20, at AM. UnKnown November 26, at PM. Newer Post Older Post Home. Subscribe to: Post Comments Atom. The upside of a view is that it will always return the latest data to you. The downside of a view is that its performance depends on how good a select statement the view is based on. If the select statement used by the view joins many tables, or uses joins based on non-indexed columns, the view could perform poorly.
They are similar to regular views, in that they are a logical view of your data based on a select statement , however, the underlying query result set has been saved to a table.
The upside of this is that when you query a materialized view, you are querying a table , which may also be indexed. In addition, because all the joins have been resolved at materialized view refresh time, you pay the price of the join once or as often as you refresh your materialized view , rather than each time you select from the materialized view.
In addition, with query rewrite enabled, Oracle can optimize a query that selects from the source of your materialized view in such a way that it instead reads from your materialized view. In situations where you create materialized views as forms of aggregate tables, or as copies of frequently executed queries, this can greatly speed up the response time of your end user application. The downside though is that the data you get back from the materialized view is only as up to date as the last time the materialized view has been refreshed.
Materialized views can be set to refresh manually, on a set schedule, or based on the database detecting a change in data from one of the underlying tables. Materialized views can be incrementally updated by combining them with materialized view logs, which act as change data capture sources on the underlying tables.
Materialized views also help to guarantee a consistent moment in time, similar to snapshot isolation. Materialized views are primarily used to increase application performance when it isn't feasible or desirable to use a standard view with indexes applied to it.
This does require a few extra permissions, but it's nothing complex. Views are essentially logical table-like structures populated on the fly by a given query. The results of a view query are not stored anywhere on disk and the view is recreated every time the query is executed.
Materialized views are actual structures stored within the database and written to disk. They are updated based on the parameters defined when they are created.
View: View is just a named query. It doesn't store anything. When there is a query on view, it runs the query of the view definition. Actual data comes from table. Materialised views: Stores data physically and get updated periodically.
While querying MV, it gives data from MV. Materialized views can only be set to refresh automatically through the database detecting changes when the view query is considered simple by the compiler.
If it's considered too complex, it won't be able to set up what are essentially internal triggers to track changes in the source tables to only update the changed rows in the mview table.
When you create a materialized view, you'll find that Oracle creates both the mview and as a table with the same name , which can make things confusing. Materialized views are the logical view of data-driven by the select query but the result of the query will get stored in the table or disk, also the definition of the query will also store in the database. The performance of Materialized view it is better than normal View because the data of materialized view will be stored in table and table may be indexed so faster for joining also joining is done at the time of materialized views refresh time so no need to every time fire join statement as in case of view.
Other difference includes in case of View we always get latest data but in case of Materialized view we need to refresh the view for getting latest data. Views have a more restrictive behavior towards a base table. Apart from these differences between views and materialized views, some other important points to keep in mind are:. Log in to leave a comment.
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