A materialized view stores the results of a query at a single point in time, unlike a view which is virtual. Materialized views can increase query performance and efficiently support remote users. They must be managed through defining, refreshing, and dropping the view. Materialized views can be read-only or updatable and use different refresh methods like complete or fast refresh.

1. Lecture 08 Materialized View
Department of Computer Science Kardan University
Materialized View
Lec-08
Prepared by
Bilal Khan

2. Lecture 08 Materialized View
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 A materialized view (MV) is a database object that
stores the results of a query at a single point in time.
Unlike a view, materialized view is not virtual.
 Materialized views are sometimes referred to as
snapshots.
 Materialized views may be stored locally or remotely in
other site.

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 Increase query performance since it contains results of a query.
 Remote materialized views are an efficient way to replicate
data at different sites compared to fully consistent distributed
data.
◦ Do not require dedicated network connection and network load is
reduced.
◦ Efficiently support remote users

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 Materialized View Management
◦ Define materialized view
◦ Refresh materialized view
 Data of a materialized view may be out-of-date and require to be
refreshed.
◦ Drop materialized view

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 Basic Syntax
CREATE MATERIALIZED VIEW view-name
BUILD [IMMEDIATE | DEFERRED]
REFRESH [FAST | COMPLETE | FORCE ]
ON [COMMIT | DEMAND ]
[ON PREBUILT TABLE]
AS
SELECT ...;

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 Types of Materialized Views
◦ Read-Only Materialized Views
◦ Updatable Materialized Views

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 Types of Materialized Views
◦ Read-Only Materialized Views
◦ Records in the MV cannot be changed by users.
◦ Eliminates the possibility of a materialized view introducing
data conflicts with the master (base tables).

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 Types of Materialized Views
◦ Updatable Materialized Views
◦ Users can make changes to the data at the materialized view
site.
◦ Changes made to an updatable materialized view are pushed
back to the master during refresh.

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 Refresh Method of Materialized Views
◦ Complete Refresh
◦ Fast Refresh
 Differential Refresh
 On Comitt

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 Materialized Views Log
◦ A materialized view log is required on a master if you want to perform a
fast refresh on materialized views based on the master. The log is used
to record changes to the master.
◦ For Example
CREATE MATERIALIZED VIEW LOG ON customer;

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 Materialized Views Log
◦ 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.
◦ This process is called incremental or fast refresh.

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 Materialized Views Log
◦ Behaviors of Materialized view by using:
 mlog$_tablename
 SELECT COUNT(*) FROM mlog$_tablename
 SELECT * FROM mlog$_tablename

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 Materialized Views Creation
◦ CREATE MATERIALIZED VIEW view_name
REFRESH FAST ON COMMIT AS
SELECT * FROM table_name;

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 Materialized Views Creation
desc user_snapshots
SELECT name, table_name, refresh_method
FROM user_snapshots;

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 Materialized Views Creation ON DEMAND
◦ CREATE MATERIALIZED VIEW view_name
REFRESH FAST ON DEMAND
AS SELECT * FROM table_name;

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 Materialized Views Creation ON DEMAND
◦ To reflect the changes of master table in
materialized view we have to execute following
code.
execute DBMS_MVIEW.REFRESH( ‘name_of_view' );

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 Materialized Views Creation using Refresh COMPLETE
◦ CREATE MATERIALIZED VIEW view_name
REFRESH COMPLETE
START WITH SYSDATE
NEXT SYSDATE + 1
AS SELECT * FROM table_name;

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 Materialized Views Creation Updatable
◦ CREATE MATERIALIZED VIEW view_name
for UPDATE
AS SELECT * FROM table_name;

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Have a Nice Day