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What is materialized view syntax?

What is materialized view syntax?

A materialized view is a database object that contains the results of a query. The FROM clause of the query can name tables, views, and other materialized views. Collectively these objects are called master tables (a replication term) or detail tables (a data warehousing term).

How do you modify a materialized view query in Oracle?

Use the ALTER MATERIALIZED VIEW statement to modify an existing materialized view in one or more of the following ways:

  1. To change its storage characteristics.
  2. To change its refresh method, mode, or time.
  3. To alter its structure so that it is a different type of materialized view.
  4. To enable or disable query rewrite. Note:

Can materialized view be updated?

You can’t insert data into a materialized view as you can with a table. To update the contents of a materialized view, you can execute a query to refresh it. This will re-execute the query used to create it. Executing this refresh query will lock the materialized view so it can’t be accessed while refreshing.

Can we perform DML operations on materialized view in Oracle?

A materialized view can be either read-only, updatable, or writeable. Users cannot perform data manipulation language (DML) statements on read-only materialized views, but they can perform DML on updatable and writeable materialized views.

Can we delete data from materialized view?

You cannot delete rows from a read-only materialized view. If you delete rows from a writable materialized view, then the database removes the rows from the underlying container table. However, the deletions are overwritten at the next refresh operation.

How do you refresh a materialized view?

To update the data in a materialized view, you can use the REFRESH MATERIALIZED VIEW statement at any time. When you use this statement, Amazon Redshift identifies changes that have taken place in the base table or tables, and then applies those changes to the materialized view.

Can we add column in materialized view Oracle?

You can’t add columns to an MV. You need to drop and recreate it. Or create a new one alongside and switch to that. You will lose any changes to T between you “dropping” the MV and re-creating it.

Can we create index on materialized view?

A materialized view can be partitioned, and you can define a materialized view on a partitioned table. You can also define one or more indexes on the materialized view. Unlike indexes, materialized views can be accessed directly using a SELECT statement.

Can we insert in materialized view?

According to the Oracle Data Warehousing Guide, it should be an insert-only materialized view: If the materialized view has one of the following, then fast refresh is supported only on conventional DML inserts and direct loads. Such a materialized view is called an insert-only materialized view.

How we can refresh materialized view?

What is complete refresh in materialized view?

The simplest form to refresh a materialized view is a Complete Refresh. It loads the contents of a materialized view from scratch. This means, if the SQL query of the materialized view has an execution time of two hours, the Complete Refresh takes at least two hours as well – or ofter even longer.

What is fast refresh in materialized view?

Materialized views can be refreshed in two ways: fast or complete. A fast refresh requires having a materialized view log on the source tables that keeps track of all changes since the last refresh, so any new refresh only has changed (updated, new, deleted) data applied to the MV.