Can we update data in materialized view Oracle?

Specify ON DEMAND if you want the materialized view to be refreshed on demand by calling one of the three DBMS_MVIEW refresh procedures. If you omit both ON COMMIT and ON DEMAND , ON DEMAND is the default. Oracle Data Warehousing Guide on the types of materialized views you can create by specifying REFRESH ON DEMAND.

What are the restrictions in updatable materialized view?

The following limitations apply to creating materialized views:

A materialized view can query only a single table.
Joins, including self-joins, are not supported.
A materialized view cannot query:
A materialized view cannot include:
Many aggregate functions are not allowed in a materialized view definition.

How do you maintain materialized views we can use?

To maintain materialized views, we can use

✅ Triggers.
Pointers.
Cascading.

Can we automate refresh of materialized views?

Set the initialization parameters and bounce the database. Create the materialized view table. Here, we specify that the materialized view will be refreshed every two hours with the refresh fast option. Instead of using DBMS_MVIEW, you can automatically refresh the MVIEW (Snapshot) using Oracle DBMS_JOB Management.

Can we do DML on materialized view?

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

How often does a materialized view update?

Unlike indexes, materialized views are not automatically updated with every data change. They must explicitly be refreshed, either on every commit, on a periodically time schedule or – typically in data warehouses – at the end of an ETL job.

What are the restrictions for fast refresh materialized views with subqueries?

General Restrictions on Fast Refresh

The materialized view must not contain references to non-repeating expressions like SYSDATE and ROWNUM.
The materialized view must not contain references to RAW or LONG RAW data types.
It cannot contain a SELECT list subquery.

What is updatable materialized view?

Updatable materialized views enable users to insert, update, and delete rows in the materialized views. When an updatable materialized view is refreshed, these changes are pushed to the master site and applied to the master table.

How do you maintain a materialized view in SQL?

Oracle Database uses these objects to maintain the materialized views in SQL data….Materialized views in SQL Syntax and Examples:

Build Immediate: Means materialized views(mv) created immediately.
Build Deferred: Means materialized views(mv) created after one refresh.
Refresh on commit:
Refresh on Demand:

How we can refresh 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.

How do I schedule a materialized view refresh?

To schedule a refresh for the materialized view, next to Repeats, select the Time Interval: Daily, Weekly, or Monthly. From the Select days menu, select Every weekday, or Every day. Specify the hour of the day. Specify the minutes.

How do you quick refresh a materialized view?

For fast refresh to be possible, the SELECT list must contain all of the GROUP BY columns (if present), and there must be a COUNT(*) and a COUNT(column) on any aggregated columns. Also, materialized view logs must be present on all tables referenced in the query that defines the materialized view.

Can you perform DML on a read only materialized view?

Users cannot perform data manipulation language (DML) statements on read-only materialized views, but they can perform DML on updatable and writeable materialized views. Note: For read-only, updatable, and writeable materialized views, the defining query of the materialized view must reference all of the primary key columns in the master.

How is a writeable materialized view created in Oracle?

A writeable materialized view is one that is created using the FORUPDATEclause but is not part of a materialized view group. Users can perform DML operations on a writeable materialized view, but if you refresh the materialized view, then these changes are not pushed back to the master and the changes are lost in the materialized view itself.

How are DML operations used in a view?

The DML operations INSERT, UPDATE, and DELETE can be performed on simple views. These operations can be used to change the data in the underlying base tables. If you create a view that allows users to view restricted information using the WHERE clause, users can still perform DML operations on all columns of the view.

How are materialized views used in Oracle replication?

Oracle uses materialized views(also known as snapshots in prior releases) to replicate data to non-master sites in a replication environment and to cache expensive queries in a data warehouse environment. This chapter, and this Oracle9i Replicationmanual in general, discusses materialized views for use in a replication environment.