The alter materialized view is used to modify an existing materialized view in one or more of the following ways. Likewise, if you specify including new values and that attribute has already been specified for the materialized view log, oracle database ignores the. Use the create materialized view statement to create a materialized view. This clause has no effect on a view that is already enabled. It is a precomputed table comprising aggregated or joined data from fact and possibly dimensions tables.
Set hidden clause use the set hidden clause to obfuscate the definition of a materialized view. For more information, see hiding materialized views enable clause use the enable clause to enable a disabled materialized view, making it available for the database server to use. The materialized view query is quite a complicated query involving a few tables, not any view, and is refreshed nightly via a job. This script will display the source for any materialized view s ee this link for a complete oracle script download. The query optimizer automatically recognizes when an existing cube mv can and should be used to satisfy a sql query was issued against a detailed fact table. To fast refresh a materialized join view, you must create a materialized view log for each of the tables referenced by the materialized views. Realtime materialized views in oracle database 12c. In oracle, if you specify refresh fast for a singletable aggregate oracle materialized view, you must have created a materialized view log for the underlying table, or the refresh command will fail. It is more efficient to use materialized views if query involves summaries, large or multiple joins or both. Materialized views are often used for summary and prejoined tables, or just to make a snapshot of a table available on a remote system.
If you alter a view that is referenced by one or more materialized views, then those materialized views are invalidated. Updatable materialized view vinayaga consultancy ltd. A materialized view stores both definitions of view plus rows resulting from the execution of the view. Unlike a view, a materialized view has a concrete existance, in the sence that the tables are prejoined and aggreations made and the results of the query are stored on disk. When a materialized view is created oracle may add system generated indexes to its underlying table i. The from clause of the query can name tables, views, and other materialized views.
You can also use materialized views to download a subset of data from central servers to mobile clients, with periodic refreshes and updates between clients. Easier, better, faster, stronger json json from sql json in plsql looooooooooong names robust code using. It more specifically overrides the start with clause, which is specified with the create materialized view command. Oracle database automatically refreshes this materialized view tomorrow at 11.
To alter its structure so that it is a different type of materialized view. A materialized view log snapshot log is a schema object that records changes to a master tables data so that a materialized view defined on that master table can be refreshed incrementally. The oracle 11g bi documentation notes the interface layer between the conceptual star schema and olap cube, and the underlying data storage layer. A materialized view is a database object that contains the results of a query. I am running oracle 11g and sql developer on the client.
Ask tom materialized view refresh data compression. Oracle uses materialized views also known as snapshots in prior releases to replicate data to nonmaster sites in a replication environment and to cache expensive queries in a data warehouse environment. To use materialized view user does not need to provide materialized view. The database also invalidates any local objects that depend on the view. Slow materialized view complete refresh issues resolved. I have a materialized view that i would like to convert into an ordinary table. Understanding materialized view in oracle skillguru. You can disable query rewrite at the system level by issuing an alter. In the following example note how oracle automatically adds an index to implement the system generated primary key we saw in the preceding topic. Manually refreshing materialized views and creating. A materialized view that supports an analytic view is very simple and efficient it only needs to select and group by the columns mapped to the key attributes of appropriate the aggregate levels.
This windforward is based on changes computed using materialized view logs, similar to a conventional fast refresh, but the operation only affect the current. The frequency of this refresh can be configured to run ondemand or at regular time intervals. Force a materialized view refresh burleson oracle consulting. If the contents of the master tables of a materialized view are modified, then the data in the materialized view must be updated to make the materialized view accurately reflect the data currently in its master tables. Materialized view contains data and additional space is required to create materialized view. A materialized view log is located in the master database in the same schema as the master table. You can also use materialized views to download a subset of data from central servers. Collectively these source objects are called master tables a replication term or detail tables a data warehousing term. In an extension of the materialized view capabilities for oracle database 11g, olap cubes can be represented as a cubeorganized materialized views cube mvs. A materialized view is similar to a view but the data is actually stored on disk view that materializes. A mv must be refreshed when the data in the underlying tables is changed. In computing, a materialized view is a database object that contains the results of a query.
Materialized view fast refreshes are slow oracle faq. 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. The landmark book advanced oracle sql tuning the definitive reference is filled with valuable information on oracle sql tuning. Ask tom how to update a materialized view directly oracle.
Oracle has devised a way to use oracle s materialized view construct to store olap cubes, much in the same fashion as materialized views are used to prejoin tables and preaggregate table data. Oracle database can use this materialized view log to perform fast refreshes for all fastrefreshable materialized views based on the master table. Convert a materialized view into a table in oracle 11g. In earlier releases before 10g the parameter was set to false by default but now it is set to true, which forces a delete of the materialized view instead of truncate, making the materialized view more available at refresh time. When creating an oracle materialized view, you have the option of specifying whether the refresh occurs manually on demand or automatically on. This chapter contains the following sql statements. I have a materialized view where i want to manually refresh the materialization. The manual refresh overtakes any previous refresh timing options, which were specified during the creation of the view. Materialized views also differ from views because they are redundant, being copied from the base tables. A master table can have only one materialized view log defined on it. A column called id part of the table t must be altered from number10 to number20. This reference uses the term master tables for consistency. Now lets take a look at how to create and manage a updatable materialized view.
Collectively these source objects are called master tables a replication term. Oracle materialized views fast refresh complete log. When you issue an alter view statement, oracle database recompiles the view regardless of whether it is valid or invalid. Updatable materialized view is useful if you are looking to replicate the changes happened on the client site to the master site. Oracle database can use this materialized view log to perform fast refreshes for all fastrefreshable materialized views based on. In this tutorial you will make a materialized view that aggregates data. A materialized view, or snapshot as they were previously known, is a table segment whose contents are periodically refreshed based on a query, either against a local or remote table. This chapter, and this oracle database advanced replication manual in general, discusses materialized views for use in a replication environment. Heres my rundown of the top 12 new features to help you when developing against oracle database. Materialized view concepts and architecture oracle.
You must be the owner of the master table or you must have the select privilege on the master table and the alter privilege on the materialized view log. Materialized views in sql examples of materialized view. Alter materialized view log for information on modifying a. For example, it may be a local copy of data located remotely, or may be a subset of the rows andor columns of a table or join result, or may be a summary using an aggregate function the process of setting up a materialized view is sometimes called materialization. All indexes and keys for the materialized view are dropped as well. If you attempt to drop, truncate, or exchange a materialized view log partition, then oracle database raises an error. The oracle database 11g server results cache, however, is in effect creating and maintaining materialized views on the fly, using a cache.
136 317 214 479 678 1267 392 547 975 507 1117 993 1550 1263 53 303 844 1536 402 678 681 999 1175 151 482 1416 557 909 870 1571 1170 1188 1138 555 850 1459 646 1305 868 598 749 945 360 696 1474 1190 476 511