what are oracle materialized views? How to use them? – complete reference for the new oracle dba

you are a new oracle dba. you want to know about materialized views and how you can create them. you also would like to know how materialized views are important for database performance tuning.you would like to know some examples on how to create materialized views.

Below article contains a complete reference on materialized views for the new oracle dba.

View is stored sql statement which would execute when ever you query on it, and it will query the base tables directly, On the other hand Materialized View, actually its a whole big topic, the key features are, it create a physical table with its own storage, its an advance form of snapshot, it could be refreshed when ever user query it, when ever the data gets commit in base tables or manually, if the user have QUERY REWRITE privilage and the materialized view has been made for getting aggrigate result in the same schema with the query rewrite option, and if the user’s select statement could get the same kind of result that you have in the materialized view then even though user is selecting base tables, but Oracle will get the result from the materialzed view.
For more information consult the following link.

http://download-west.oracle.com/docs/cd/B10501_01/server.920/a96520/mv.htm#42135

CREATE MATERIALIZED VIEW mv_simple_sri

TABLESPACE ts_users

BUILD IMMEDIATE

REFRESH force ON demand AS

SELECT * FROM sri_test;

select * from dba_users where username=user

select * from dba_objects where owner=’KADIYAL’

create table sri_test(a number , b number);

alter table sri_test add primary key(a )

insert into sri_test

select rownum,rownum+100 from dba_objects where rownum < 10000

commit;

BEGIN

Exec dbms_mview.refresh(‘minddba.MV_RAS_HIERARCHY’);

END;

EXECUTE DBMS_MVIEW.EXPLAIN_MVIEW ('SH.CAL_MONTH_SALES_MV');

select * from dba_mviews

select query from dba_mviews where mview_name = ‘ECLAIM_REF_SAP’ and owner = ‘EOI’

SELECT table_name,master,last_refresh FROM ALL_SNAPSHOTS WHERE OWNER=’EOI’ ORDER BY LAST_REFRESH;

select OWNER,MVIEW_NAME,UPDATABLE,STALENESS,COMPILE_STATE from dba_mviews

where compile_state=’NEEDS_COMPILE’

Please find below

1)to find out all snap shot sites (other databases that refer to our c_history table )

select * from DBA_REGISTERED_snapshots where name like ‘%HISTORY%’

2) Next in the output from above query please verify in the column snapshot_site the snap shot sites and populate the value

in below query.

To unregister please run each of these blocks individually in toad

begin

dbms_mview.unregister_snapshot(‘CON’,’C_HISTORY’,’TRT.WORLD’);

end;

begin

dbms_mview.unregister_snapshot(‘CON’,’C_HISTORY’,’WAFD.COM’);

end;

begin

dbms_mview.unregister_snapshot(‘CON’,’C_HISTORY’,’DRB.COM’);

end;

to find out materialized views in current database where I pass the table name

declare

p_get_dep_mv varchar2(4000);

begin

dbms_mview.get_mv_dependencies(‘con.c_history’, p_get_dep_mv);

dbms_output.put_line(p_get_dep_mv);

dbms_output.put_line(‘sridhar’);

end;

–created the primary key on the dummy table

create materialized view log on dummy with primary key;

create materialized view MV_F_REAL

on prebuilt table

refresh complete

as select * from dummy

select * from MV_F_REAL

select * from user_objects where object_name like ‘%MV%’

drop table mv_f_real

drop

Please find below the detailed syntax for materialized views from psoug.org.

Oracle Materialized Views

Version 10.2

General

Data Dictionary Objects

col$	snap$	tab$

DBA	ALL	USER
dba_base_table_mviews	all_base_table_mviews	user_base_table_mviews
dba_mview_log _filter_cols
dba_mviews	all_mviews	user_mviews
dba_mview_aggregates	all_mview_aggregates	user_mview_aggregates
dba_mview_analysis	all_mview_analysis	user_mview_analysis
dba_mview_comments	all_mview_comments	user_mview_comments
dba_mview_detail_relations	all_mview_detail_relations	user_mview_detail_relations
dba_mview_joins	all_mview_joins	user_mview_joins
dba_mview_keys	all_mview_keys	user_mview_keys
dba_mview_logs	all_mview_logs	user_mview_logs
dba_mview_refresh_times	all_mview_refresh_times	user_mview_refresh_times
	all_refresh_dependencies
dba_registered_mview_groups
dba_registered_mviews	all_registered_mviews	user_registered_mviews
dba_registered_snapshot_groups
dba_tune_mview		user_tune_mview

Related Packages

dbms_offline_snapshot	dbms_snapshot_lib
dbms_snapshot	dbms_snapshot_util

System Privileges

create materialized view
create any materialized view
drop any materialized view

delete any table

insert any table
lock any table
select any table
under any table
update any table

create table
create view

Definitions

Complex Materialized View

Each row in the materialized view can not be mapped back to a single row in a source table.

Materialized View

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). This reference uses "master tables" for consistency. The databases containing the master tables are called the master databases.

When you create a materialized view, Oracle Database creates one internal table and at least one index, and may create one view, all in the schema of the materialized view. Oracle Database uses these objects to maintain the materialized view data. You must have the privileges necessary to create these objects.

Materialized View 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. Without a materialized view log, Oracle Database must re-execute the materialized view query to refresh the materialized view. This process is called a complete refresh. Usually, a fast refresh takes less time than a complete refresh.

A materialized view log is located in the master database in the same schema as the master table. A master table can have only one materialized view log defined on it. Oracle Database can use this materialized view log to perform fast refreshes for all fast-refreshable materialized views based on the master table.

To fast refresh a materialized join view, you must create a materialized view log for each of the tables referenced by the materialized view.

Build

Specifies when to populate the materialized view. Specify IMMEDIATE to indicate that the materialized view is to be populated immediately: The default. Specify DEFERRED to indicate that the materialized view is to be populated by the next REFRESH operation. The first (deferred) refresh must always be a complete refresh. Until then, the materialized view has a staleness value of UNUSABLE, so it cannot be used for query rewrite.

Syntax: BUILD <IMMEDIATE | DEFERRED>

WITH REDUCED PRECISION	Authorizes the loss of precision that will result if the precision of the table or materialized view columns do not exactly match the precision returned by subquery.
WITHOUT REDUCED PRECISION	Requires that the precision of the table or materialized view columns match exactly the precision returned by the subquery, or the create operation will fail. This is the default

Caching

For data that will be accessed frequently, CACHE specifies that the blocks retrieved for this table are placed at the most recently used end of the least recently used (LRU) list in the buffer cache when a full table scan is performed. This attribute is useful for small lookup tables. NOCACHE specifies that the blocks are placed at the least recently used end of the LRU list.

Syntax: <CACHE | NOCACHE>

Cluster

Creates materialized views as part of a cluster. A cluster materialized view uses the space allocation of the cluster. Partitioning is not allowed when an MV is built on a cluster.

Compression

Use the table_compression clause to instruct the database whether to compress data segments to reduce disk and memory use. The COMPRESS keyword enables table compression. The NOCOMPRESS keyword disables table compression.

Syntax: <COMPRESS | NOCOMPRESS>

Organization Index

Create an index-organized materialized view. IOT can be specified for the following:

Read-only and updatable object materialized views.
Read-only and updatable primary key materialized views.
Read-only rowid materialized views.

The keywords and parameters of the index_org_table_clause have the same semantics as described in CREATE TABLE, with the restrictions that follow.

Parallel

The parallel_clause indicates whether parallel operations will be supported for the materialized view and sets the default degree of parallelism for queries and DML on the materialized view after creation.

Syntax: PARALLEL (DEGREE <INTEGER>)

Partitioning

Prebuilt Tables

The ON PREBUILT TABLE clause lets you register an existing table as a preinitialized materialized view. This clause is particularly useful for registering large materialized views in a data warehousing environment. The table must have the same name and be in the same schema as the resulting materialized view.

If the materialized view is dropped, then the preexisting table reverts to its identity as a table.

Query Rewrite

If the schema owner does not own the master tables, then the schema owner must have the GLOBAL QUERY REWRITE privilege or the QUERY REWRITE object privilege on each table outside the schema.

If you are defining the materialized view on a pre-built container (ON PRE-BUILT TABLE clause), then you must have the SELECT privilege WITH GRANT OPTION on the container table.

Refresh Group

A grouping of materialized views so that they can be refreshed as a single transaction for consistency

Refresh Log

Refresh Types

COMPLETE REFRESH
FAST REFRESH

Simple Materialized View

Each row in the materialized view can be mapped back to a single row in a source table

Snapshot

The keyword SNAPSHOT is supported in place of MATERIALIZED VIEW for backward compatibility

Using Index

The USING INDEX claause allow establishing values for INITRANS and STORAGE parameters for the default index used to maintain the materialized view. If USING INDEX is not specified, then default tablespace values are used. The default index is used to speed up incremental (FAST) refresh of the materialized view.

Specify USING NO INDEX to suppress the creation of the default index. You can create an alternative index explicitly by using the CREATE INDEX statement. You should create such an index if you specify USING NO INDEX and you are creating the materialized view with the incremental refresh method (REFRESH FAST).

Syntax: <USING INDEX | USING NO INDEX>

Create Materialized View

Fast Refresh

CREATE MATERIALIZED VIEW <schema.name>
PCTFREE <integer>
PCTUSED <integer>
TABLESPACE <tablespace_name>
BUILD IMMEDIATE
REFRESH <FAST | FORCE> ON <COMMIT | DEMAND>
<USING INDEX | USING NO INDEX>
INITRANS <integer>
STORAGE CLAUSE
AS (<SQL statement>);

CREATE MATERIALIZED VIEW mv_simple
TABLESPACE uwdata
BUILD IMMEDIATE
REFRESH FAST ON COMMIT AS
SELECT * FROM servers;

— create refresh log then repeat
SELECT name, table_name, updatable, refresh_method,
refresh_mode
FROM user_snapshots;

set long 10000

SELECT name, query
FROM user_snapshots;

SELECT name, last_refresh
FROM user_mview_refresh_times;

SELECT table_name
FROM user_tables;

SELECT constraint_name, table_name, constraint_type
FROM user_constraints;

SELECT DISTINCT network_id
FROM servers;

SELECT DISTINCT network_id
FROM mv_simple;

UPDATE servers
SET network_id = 10
WHERE network_id = 6;

SELECT DISTINCT network_id
FROM servers;

SELECT DISTINCT network_id
FROM mv_simple;

COMMIT;

SELECT DISTINCT network_id
FROM servers;

SELECT DISTINCT network_id
FROM mv_simple;

Force Refresh

CREATE MATERIALIZED VIEW <schema.name>
PCTFREE <integer>
PCTUSED <integer>
TABLESPACE <tablespace_name>
BUILD IMMEDIATE
REFRESH <FAST | FORCE> ON <COMMIT | DEMAND>
AS (<SQL statement>);

CREATE MATERIALIZED VIEW mv_force
TABLESPACE uwdata
NOCACHE
LOGGING
NOCOMPRESS
NOPARALLEL
BUILD IMMEDIATE
REFRESH FORCE ON DEMAND
WITH ROWID AS
SELECT * FROM servers;

desc mv_force

SELECT name, table_name, updatable, refresh_method,
refresh_mode
FROM user_snapshots;

set long 10000

SELECT name, query
FROM user_snapshots;

Complete Refresh

CREATE MATERIALIZED VIEW <schema.name>
PCTFREE <integer>
PCTUSED <integer>
TABLESPACE <tablespace_name>
REFRESH <COMPLETE | FORCE>
START WITH <date>
NEXT <date_calculation>
[FOR UPDATE]
AS (<SQL statement>);

CREATE MATERIALIZED VIEW mv_complete
TABLESPACE uwdata
REFRESH COMPLETE
START WITH SYSDATE
NEXT SYSDATE + 1
AS SELECT s.srvr_id, i.installstatus, COUNT(*)
FROM servers s, serv_inst i
WHERE s.srvr_id = i.srvr_id
GROUP BY s.srvr_id, i.installstatus;

Note: To create a materialized view that refreshes at 3:00am in the morning:

SQL> SELECT to_char(sysdate, ‘MM/DD/YYYY HH:MI:SS’)
2 FROM dual;

TO_CHAR(SYSDATE,’MM/DD/YYYYHH
—————————————————————–
12/03/2006 01:25:30

SQL> SELECT TO_CHAR(TRUNC(SYSDATE) + 3/24, ‘MM/DD/YYYY HH:MI:SS’)
2 FROM dual;

TO_CHAR(TRUNC(SYSDATE)+3/24,’M
—————————————————————–
12/03/2006 03:00:00

SELECT name, table_name, updatable, refresh_method
FROM user_snapshots;

SELECT name, table_name,
refresh_method
FROM user_snapshots;

col next format a30

SELECT name, type, next, start_with, refresh_group
FROM user_snapshots;

col query format a50

SELECT name, query, status
FROM user_snapshots;

SELECT *
FROM mv_complete

Complete Refresh Using Index

CREATE MATERIALIZED VIEW <schema.name>
[LOGGING] [CACHE]
PCTFREE <integer>
PCTUSED <integer>
USING INDEX
TABLESPACE <tablespace_name>
REFRESH <COMPLETE | FORCE>
START WITH <date>
NEXT <date_calculation>
[FOR UPDATE]
AS (<SQL statement>);

CREATE SNAPSHOT mv_w_index
LOGGING CACHE
PCTFREE 0 PCTUSED 99
TABLESPACE uwdata
REFRESH COMPLETE
AS SELECT s.srvr_id, COUNT(*)
FROM servers s, serv_inst i
WHERE s.srvr_id = i.srvr_id
GROUP BY s.srvr_id;

desc mv_w_index

SELECT * FROM mv_w_index;

SELECT index_name, index_type
FROM user_indexes;

SELECT column_expression
FROM user_ind_expressions
WHERE table_name = ‘MV_W_INDEX’;

Prebuilt Table

conn sh/sh

CREATE TABLE mv_prebuilt (
month VARCHAR2(8),
state VARCHAR2(40),
sales NUMBER(10,2));

CREATE MATERIALIZED VIEW mv_prebuilt
ON PREBUILT TABLE WITH REDUCED PRECISION
AS SELECT t.calendar_month_desc AS month,
c.cust_state_province AS state,
SUM(s.amount_sold) AS sales
FROM times t, customers c, sales s
WHERE s.time_id = t.time_id AND s.cust_id = c.cust_id
GROUP BY t.calendar_month_desc, c.cust_state_province;

Enable Query Rewrite

set linesize 121
col name format a30
col value format a30

SELECT name, value
FROM gv$parameter
WHERE name LIKE ‘%rewrite%’;

EXPLAIN PLAN FOR
SELECT s.srvr_id, i.installstatus, COUNT(*)
FROM servers s, serv_inst i
WHERE s.srvr_id = i.srvr_id
AND s.srvr_id = 502
GROUP BY s.srvr_id, i.installstatus;

SELECT * FROM TABLE(dbms_xplan.display);

CREATE MATERIALIZED VIEW mv_rewrite
TABLESPACE uwdata
REFRESH ON DEMAND
ENABLE QUERY REWRITE
AS SELECT s.srvr_id, i.installstatus, COUNT(*)
FROM servers s, serv_inst i
WHERE s.srvr_id = i.srvr_id
GROUP BY s.srvr_id, i.installstatus;

EXPLAIN PLAN FOR
SELECT s.srvr_id, i.installstatus, COUNT(*)
FROM servers s, serv_inst i
WHERE s.srvr_id = i.srvr_id
AND s.srvr_id = 502
GROUP BY s.srvr_id, i.installstatus;

SELECT * FROM TABLE(dbms_xplan.display);

— if the base table may be updated then
ALTER SESSION SET query_rewrite_integrity = STALE_TOLERATED;

Alter Materialized View

Allocate Extent

ALTER MATERIALIZED VIEW <schema.materialized_view>
ALLOCATE EXTENT (SIZE <size_clause> DATAFILE <‘file_name’>)
INSTANCE <integer>;

ALTER MATERIALIZED VIEW mv_simple ALLOCATE EXTENT (SIZE 8K);

Caching

ALTER MATERIALIZED VIEW <schema.materialized_view>
<CACHE | NOCACHE>;

ALTER MATERIALIZED VIEW mv_simple NOCACHE;

Compile

ALTER MATERIALIZED VIEW <schema.materialized_view> COMPILE;

ALTER MATERIALIZED VIEW mv_simple COMPILE;

Consider Fresh

ALTER MATERIALIZED VIEW <schema.materialized_view>
CONSIDER FRESH;

ALTER MATERIALIZED VIEW mv_complete CONSIDER FRESH;

Deallocate Unused

ALTER MATERIALIZED VIEW <schema.materialized_view>
DEALLOCATE UNUSED;

ALTER MATERIALIZED VIEW mv_complete DEALLOCATE UNUSED;

Index Organized Table

ALTER MATERIALIZED VIEW <schema.materialized_view>
<index_organized_table_clause>
<alter_overflow_clause>
<alter_mapping_table_clause>
COALESCE;

See IOT Page;

LOB Storage

ALTER MATERIALIZED VIEW <schema.materialized_view>
LOB (lob_item) STORE AS (lob_storage_parameters);

TBD

Logging

ALTER MATERIALIZED VIEW <schema.materialized_view>
<LOGGING | NOLOGGING>;

ALTER MATERIALIZED VIEW mv_simple LOGGING;

Modify LOB Storage

ALTER MATERIALIZED VIEW <schema.materialized_view>
MODIFY LOB (<lob_item>) (new_lob_parameter);

TBD

Parallel Access

ALTER MATERIALIZED VIEW <schema.materialized_view>
<PARALLEL | NO_PARALLEL>;

ALTER MATERIALIZED VIEW mv_simple PARALLEL;

Physical Attributes

ALTER MATERIALIZED VIEW <schema.materialized_view> (
PCT_FREE <integer>
PCT_USED <integer>
INITRANS <integer>
TABLESPACE <tablespace_name>;

ALTER MATERIALIZED VIEW mv_simple PCTFREE 1;

Query Rewrite

ALTER MATERIALIZED VIEW <schema.materialized_view>
<ENABLE | DISABLE> QUERY REWRITE;

ALTER MATERIALIZED VIEW mv_simple ENABLE QUERY REWRITE;

Refresh

ALTER MATERIALIZED VIEW <schema.materialized_view>
REFRESH <FAST | COMPLETE | FORCE>
ON <DEMAND | COMMIT>
START WITH <date_time>
NEXT <date_time>
WITH PRIMARY KEY
USING DEFAULT MASTER ROLLBACK SEGMENT
USING <ENFORCED | TRUSTED> CONSTRAINTS;

ALTER MATERIALIZED VIEW mv_complete REFRESH COMPLETE;

Shrink

ALTER MATERIALIZED VIEW <schema.materialized_view> SHRINK SPACE <COMPACT | CASCADE>;

ALTER MATERIALIZED VIEW mv_simple ENABLE ROW MOVEMENT;

ALTER MATERIALIZED VIEW mv_simple SHRINK SPACE CASCADE;

Table Compression

ALTER MATERIALIZED VIEW <schema.materialized_view>
<COMPRESS | NOCOMPRESS>;

ALTER MATERIALIZED VIEW mv_simple COMPRESS;

Table Partitioning

ALTER MATERIALIZED VIEW <schema.materialized_view> ….

See Partitioning Page;

Drop

Drop Materialized View

DROP MATERIALIZED VIEW <schema.materialized_view>;

SELECT table_name
FROM user_tables;

DROP MATERIALIZED VIEW mv_simple;

SELECT table_name
FROM user_tables;

Drop Materialized View
Preserve Table

DROP MATERIALIZED VIEW <schema.materialized_view>
PRESERVE TABLE;

SELECT table_name
FROM user_tables;

DROP MATERIALIZED VIEW mv_simple PRESERVE TABLE;

SELECT table_name
FROM user_tables;

DROP TABLE mv_serers;

SELECT table_name
FROM user_tables;

Create Refresh Log

Create Log

CREATE MATERIALIZED VIEW LOG ON servers
PCTFREE 0
PCTUSED 99
TABLESPACE uwdata
WITH PRIMARY KEY, ROWID;

SELECT master, log_table, rowids, primary_key
FROM user_snapshot_logs;

SELECT table_name
FROM user_tables;

Alter Refresh Log

Alter Physical Attributes

ALTER MATERIALIZED VIEW LOG [FORCE] ON <schema.table_name>
PCTFREE <integer>
PCTUSED <integer>
TABLESPACE <tablespace_name>;

SELECT table_name, pct_free, pct_used
FROM user_tables;

ALTER MATERIALIZED VIEW LOG ON servers PCTFREE 20;

SELECT table_name, pct_free, pct_used
FROM user_tables;

Alter Parallelism

ALTER MATERIALIZED VIEW LOG [FORCE] ON <schema.table_name>
<NOPARALLEL | PARALLEL <integer>>;

SELECT table_name, degree
FROM user_tables;

ALTER MATERIALIZED VIEW LOG ON servers PARALLEL 8;

SELECT table_name, degree
FROM user_tables;

Alter Logging

ALTER MATERIALIZED VIEW LOG [FORCE] ON <schema.table_name>
<LOGGING | NOLOGGING>;

ALTER MATERIALIZED VIEW LOG ON servers LOGGING;

Alter Allocate Extent by Size

ALTER MATERIALIZED VIEW LOG [FORCE] ON <schema.table_name>
ALLOCATE EXTENT (SIZE <integer> <M | G | T>);

ALTER MATERIALIZED VIEW LOG ON servers
ALLOCATE EXTENT (SIZE 512K);

Alter Allocate Extent by Datafile

ALTER MATERIALIZED VIEW LOG [FORCE] ON <schema.table_name>
ALLOCATE EXTENT (DATAFILE <file_name>);

ALTER MATERIALIZED VIEW LOG ON servers
ALLOCATE EXTENT (DATAFILE ‘c:\temp\users01.dbf’);

Alter Allocate Extent by Instance

ALTER MATERIALIZED VIEW LOG [FORCE] ON <schema.table_name>
ALLOCATE EXTENT SIZE (INSTANCE <integer>);

ALTER MATERIALIZED VIEW LOG ON servers
ALLOCATE EXTENT (INSTANCE 1);

Shrink Log

ALTER MATERIALIZED VIEW LOG [FORCE] ON <schema.table_name>
[COMPACT] [CASCADE];

ALTER MATERIALIZED VIEW LOG ON servers
SHRINK SPACE COMPACT CASCADE;

ALTER TABLE mlog$_servers ENABLE ROW MOVEMENT;

ALTER MATERIALIZED VIEW LOG ON servers
SHRINK SPACE COMPACT CASCADE;

Log Caching

ALTER MATERIALIZED VIEW LOG [FORCE] ON <schema.table_name>
<CACHE | NOCACHE>;

ALTER MATERIALIZED VIEW LOG ON servers CACHE;

Add Clause

ALTER MATERIALIZED VIEW LOG ON servers ADD SEQUENCE;

Drop Refresh Log

Drop Log

DROP MATERIALIZED VIEW LOG ON <table_name>;

DROP MATERIALIZED VIEW LOG ON servers;

Related Topics

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