Oracle® Database SQL Language Reference 11g Release 2 (11.2) Part Number E17118-04 |
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Use the CREATE
MATERIALIZED
VIEW
statement to create a 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.
Note:
The keywordSNAPSHOT
is supported in place of MATERIALIZED
VIEW
for backward compatibility.For replication purposes, materialized views allow you to maintain copies of remote data on your local node. The copies can be updatable with the Advanced Replication feature and are read-only without this feature. You can select data from a materialized view as you would from a table or view. In replication environments, the materialized views commonly created are primary key, rowid, object, and subquery materialized views.
See Also:
Oracle Database Advanced Replication for information on the types of materialized views used to support replicationFor data warehousing purposes, the materialized views commonly created are materialized aggregate views, single-table materialized aggregate views, and materialized join views. All three types of materialized views can be used by query rewrite, an optimization technique that transforms a user request written in terms of master tables into a semantically equivalent request that includes one or more materialized views.
See Also:
Oracle Database Data Warehousing Guide for information on the types of materialized views used to support data warehousing
The privileges required to create a materialized view should be granted directly rather than through a role.
To create a materialized view in your own schema:
You must have been granted the CREATE
MATERIALIZED
VIEW
system privilege and either the CREATE
TABLE
or CREATE
ANY
TABLE
system privilege.
You must also have access to any master tables of the materialized view that you do not own, either through a SELECT
object privilege on each of the tables or through the SELECT
ANY
TABLE
system privilege.
To create a materialized view in another user's schema:
You must have the CREATE
ANY
MATERIALIZED
VIEW
system privilege.
The owner of the materialized view must have the CREATE
TABLE
system privilege. The owner must also have access to any master tables of the materialized view that the schema owner does not own (for example, if the master tables are on a remote database) and to any materialized view logs defined on those master tables, either through a SELECT
object privilege on each of the tables or through the SELECT
ANY
TABLE
system privilege.
To create a refresh-on-commit materialized view (ON
COMMIT
REFRESH
clause), in addition to the preceding privileges, you must have the ON
COMMIT
REFRESH
object privilege on any master tables that you do not own or you must have the ON
COMMIT
REFRESH
system privilege.
To create the materialized view with query rewrite enabled, in addition to the preceding privileges:
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 prebuilt container (ON
PREBUILT
TABLE
clause), then you must have the SELECT
privilege WITH
GRANT
OPTION
on the container table.
The user whose schema contains the materialized view must have sufficient quota in the target tablespace to store the master table and index of the materialized view or must have the UNLIMITED
TABLESPACE
system privilege.
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.
You can create the following types of local materialized views (including both ON
COMMIT
and ON
DEMAND
) on master tables with commit SCN-based materialized view logs:
Materialized aggregate views, including materialized aggregate views on a single table
Materialized join views
Primary-key-based and rowid-based single table materialized views
UNION
ALL
materialized views, where each UNION
ALL
branch is one of the above materialized view types
You cannot create remote materialized views on master tables with commit SCN-based materialized view logs.
Creating a materialized view on master tables with different types of materialized view logs (that is, a master table with timestamp-based materialized view logs and a master table with commit SCN-based materialized view logs) is not supported and causes ORA-32414
.
See Also:
CREATE TABLE, CREATE VIEW, and CREATE INDEX for information on these privileges
Oracle Database Advanced Replication for information about the prerequisites that apply to creating replication materialized views
Oracle Database Data Warehousing Guide for information about the prerequisites that apply to creating data warehousing materialized views
(physical_properties::=, scoped_table_ref_constraint ::=, materialized_view_props::=, physical_attributes_clause::=, create_mv_refresh::=, subquery::=)
(deferred_segment_creation::=, segment_attributes_clause::=, table_compression ::=, index_org_table_clause::=)
(column_properties ::=, table_partitioning_clauses ::=—part of CREATE
TABLE
syntax, parallel_clause::=, build_clause::=)
scoped_table_ref_constraint ::=
(mapping_table_clause
: not supported with materialized views, key_compression::=, index_org_overflow_clause::=)
(segment_attributes_clause::=)
(physical_attributes_clause::=, logging_clause::=)
(
object_type_col_properties::=, nested_table_col_properties::=, varray_col_properties::=, LOB_partition_storage::=, LOB_storage_clause::=, XMLType_column_properties
: not supported for materialized views)
(substitutable_column_clause::=)
substitutable_column_clause::=
nested_table_col_properties::=
(substitutable_column_clause::=, object_properties::=, physical_properties::=—part of CREATE
TABLE
syntax, column_properties ::=)
(substitutable_column_clause::=, varray_storage_clause::=)
(LOB_parameters::=, storage_clause::=)
(storage_clause::=, logging_clause::=)
(LOB_storage_clause::=, varray_col_properties::=)
build_clause::=
Specify the schema to contain the materialized view. If you omit schema
, then Oracle Database creates the materialized view in your schema.
Specify the name of the materialized view to be created. Oracle Database generates names for the table and indexes used to maintain the materialized view by adding a prefix or suffix to the materialized view name.
You can specify a column alias for each column of the materialized view. The column alias list explicitly resolves any column name conflict, eliminating the need to specify aliases in the SELECT
clause of the materialized view. If you specify any column alias in this clause, then you must specify an alias for each data source referenced in the SELECT
clause.
Use this clause to encrypt this column of the materialized view. Please refer to the CREATE
TABLE
clause encryption_spec for more information on column encryption.
The OF
object_type
clause lets you explicitly create an object materialized view of type object_type
.
Use the SCOPE
FOR
clause to restrict the scope of references to a single object table. You can refer either to the table name with scope_table_name
or to a column alias. The values in the REF
column or attribute point to objects in scope_table_name
or c_alias
, in which object instances of the same type as the REF
column are stored. If you specify aliases, then they must have a one-to-one correspondence with the columns in the SELECT
list of the defining query of the materialized view.
See Also:
"SCOPE REF Constraints" for more informationThe 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.
Caution:
This clause assumes that the table object reflects the materialization of a subquery. Oracle strongly recommends that you ensure that this assumption is true in order to ensure that the materialized view correctly reflects the data in its master tables.The ON
PREBUILT
TABLE
clause could be useful in the following scenarios:
You have a table representing the result of a query. Creating the table was an expensive operation that possibly took a long time. You want to create a materialized view on the query. You can use the ON
PREBUILT
TABLE
clause to avoid the expense of executing the query and populating the container for the materialized view.
You temporarily discontinue having a materialized view, but keep its container table, using the DROP
MATERIALIZED
VIEW
... PRESERVE
TABLE
statement. You then decide to recreate the materialized view and you know that the master tables of the view have not changed. You can create the materialized view using the ON
PREBUILT
TABLE
clause. This avoids the expense and time of creating and populating the container table for the materialized view.
WITH REDUCED PRECISION Specify WITH
REDUCED
PRECISION
to authorize 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 Specify WITHOUT
REDUCED
PRECISION
to require that the precision of the table or materialized view columns match exactly the precision returned by subquery
, or the create operation will fail. This is the default.
Restrictions on Using Prebuilt Tables Prebuilt tables are subject to the following restrictions:
Each column alias in subquery
must correspond to a column in the prebuilt table, and corresponding columns must have matching data types.
If you specify this clause, then you cannot specify a NOT
NULL
constraint for any column that is not referenced in subquery
unless you also specify a default value for that column.
The components of the physical_properties_clause
have the same semantics for materialized views that they have for tables, with exceptions and additions described in the sections that follow.
Restriction on the physical_properties_clause You cannot specify ORGANIZATION
EXTERNAL
for a materialized view.
Use this clause to determine when the segment for this materialized view should be created. See the CREATE
TABLE
clause deferred_segment_creation for more information.
Use the segment_attributes_clause
to establish values for the PCTFREE
, PCTUSED
, and INITRANS
parameters, the storage characteristics for the materialized view, to assign a tablespace, and to specify whether logging is to occur. In the USING
INDEX
clause, you cannot specify PCTFREE
or PCTUSED
.
TABLESPACE Clause Specify the tablespace in which the materialized view is to be created. If you omit this clause, then Oracle Database creates the materialized view in the default tablespace of the schema containing the materialized view.
See Also:
physical_attributes_clause and storage_clause for a complete description of these clauses, including default valueslogging_clause Specify LOGGING
or NOLOGGING
to establish the logging characteristics for the materialized view. The logging characteristic affects the creation of the materialized view and any nonatomic refresh that is initiated by way of the DBMS_REFRESH
package. The default is the logging characteristic of the tablespace in which the materialized view resides.
See Also:
logging_clause for a full description of this clause and Oracle Database PL/SQL Packages and Types Reference for more information on atomic and nonatomic refreshUse the table_compression
clause to instruct the database whether to compress data segments to reduce disk and memory use.
The ORGANIZATION
INDEX
clause lets you create an index-organized materialized view. In such a materialized view, data rows are stored in an index defined on the primary key of the materialized view. You can specify index organization for the following types of materialized views:
Read-only and updatable object materialized views. You must ensure that the master table has a primary key.
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.
Restrictions on Index-Organized Materialized Views Index-organized materialized views are subject to the following restrictions:
You cannot specify the following CREATE
MATERIALIZED
VIEW
clauses: CACHE
or NOCACHE
, CLUSTER
, or ON
PREBUILT
TABLE
.
In the index_org_table_clause
:
You cannot specify the mapping_table_clause
.
You can specify COMPRESS
only for a materialized view based on a composite primary key. You can specify NOCOMPRESS
for a materialized view based on either a simple or composite primary key.
The CLUSTER
clause lets you create the materialized view as part of the specified cluster. A cluster materialized view uses the space allocation of the cluster. Therefore, you do not specify physical attributes or the TABLESPACE
clause with the CLUSTER
clause.
Restriction on Cluster Materialized Views If you specify CLUSTER
, then you cannot specify the table_partitioning_clauses
in materialized_view_props
.
Use these property clauses to describe a materialized view that is not based on an existing table. To create a materialized view that is based on an existing table, use the ON
PREBUILT
TABLE
clause.
The column_properties
clause lets you specify the storage characteristics of a LOB, nested table, varray, or XMLType
column. The object_type_col_properties
are not relevant for a materialized view.
See Also:
CREATE TABLE for detailed information about specifying the parameters of this clauseThe table_partitioning_clauses
let you specify that the materialized view is partitioned on specified ranges of values or on a hash function. Partitioning of materialized views is the same as partitioning of tables.
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.
Note:
NOCACHE
has no effect on materialized views for which you specify KEEP
in the storage_clause
.The parallel_clause
lets you indicate 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.
For complete information on this clause, refer to parallel_clause in the documentation on CREATE
TABLE
.
The build_clause
lets you specify when to populate the materialized view.
IMMEDIATE Specify IMMEDIATE
to indicate that the materialized view is to be populated immediately. This is the default.
DEFERRED 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.
The USING
INDEX
clause lets you establish the value of the INITRANS
and STORAGE
parameters for the default index Oracle Database uses to maintain the materialized view data. If USING
INDEX
is not specified, then default values are used for the index. Oracle Database uses the default index to speed up incremental (FAST
) refresh of the materialized view.
Restriction on USING INDEX clause You cannot specify the PCTUSED
parameter in this clause.
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
).
Use the create_mv_refresh
clause to specify the default methods, modes, and times for the database to refresh the materialized view. If 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. This clause lets you schedule the times and specify the method and mode for the database to refresh the materialized view.
Note:
This clause only sets the default refresh options. For instructions on actually implementing the refresh, refer to Oracle Database Advanced Replication and Oracle Database Data Warehousing Guide.See Also:
"Periodic Refresh of Materialized Views: Example" and "Automatic Refresh Times for Materialized Views: Example"
Oracle Database PL/SQL Packages and Types Reference for more information on refresh methods
Specify FAST
to indicate the incremental refresh method, which performs the refresh according to the changes that have occurred to the master tables. The changes for conventional DML changes are stored in the materialized view log associated with the master table. The changes for direct-path INSERT
operations are stored in the direct loader log.
If you specify REFRESH
FAST
, then the CREATE
statement will fail unless materialized view logs already exist for the materialized view master tables. Oracle Database creates the direct loader log automatically when a direct-path INSERT
takes place. No user intervention is needed.
For both conventional DML changes and for direct-path INSERT
operations, other conditions may restrict the eligibility of a materialized view for fast refresh.
Materialized views are not eligible for fast refresh if the defining query contains an analytic function.
See Also:
Oracle Database Advanced Replication for restrictions on fast refresh in replication environments
Oracle Database Data Warehousing Guide for restrictions on fast refresh in data warehousing environments
The EXPLAIN_MVIEW
procedure of the DBMS_MVIEW
package for help diagnosing problems with fast refresh and the TUNE_MVIEW
procedure of the DBMS_MVIEW
package correction of fast refresh problems
Specify COMPLETE
to indicate the complete refresh method, which is implemented by executing the defining query of the materialized view. If you request a complete refresh, then Oracle Database performs a complete refresh even if a fast refresh is possible.
Specify FORCE
to indicate that when a refresh occurs, Oracle Database will perform a fast refresh if one is possible or a complete refresh if fast refresh is not possible. If you do not specify a refresh method (FAST
, COMPLETE
, or FORCE
), then FORCE
is the default.
Specify ON
COMMIT
to indicate that a fast refresh is to occur whenever the database commits a transaction that operates on a master table of the materialized view. This clause may increase the time taken to complete the commit, because the database performs the refresh operation as part of the commit process.
You cannot specify both ON
COMMIT
and ON
DEMAND
. If you specify ON
COMMIT
, then you cannot also specify START
WITH
or NEXT
.
Restrictions on Refreshing ON COMMIT
This clause is not supported for materialized views containing object types or Oracle-supplied types.
This clause is not supported for materialized views with remote tables.
If you specify this clause, then you cannot subsequently execute a distributed transaction on any master table of this materialized view. For example, you cannot insert into the master by selecting from a remote table. The ON
DEMAND
clause does not impose this restriction on subsequent distributed transactions on master tables.
Specify ON
DEMAND
to indicate that database will not refresh the materialized view unless the user manually launches a refresh through one of the three DBMS_MVIEW
refresh procedures.
You cannot specify both ON
COMMIT
and ON
DEMAND
. If you omit both ON
COMMIT
and ON
DEMAND
, then ON
DEMAND
is the default. You can override this default setting by specifying the START
WITH
or NEXT
clauses, either in the same CREATE
MATERIALIZED
VIEW
statement or a subsequent ALTER
MATERIALIZED
VIEW
statement.
START
WITH
and NEXT
take precedence over ON
DEMAND
. Therefore, in most circumstances it is not meaningful to specify ON
DEMAND
when you have specified START
WITH
or NEXT
.
See Also:
Oracle Database PL/SQL Packages and Types Reference for information on these procedures
Oracle Database Data Warehousing Guide on the types of materialized views you can create by specifying REFRESH
ON
DEMAND
Specify a datetime expression for the first automatic refresh time.
Specify a datetime expression for calculating the interval between automatic refreshes.
Both the START
WITH
and NEXT
values must evaluate to a time in the future. If you omit the START
WITH
value, then the database determines the first automatic refresh time by evaluating the NEXT
expression with respect to the creation time of the materialized view. If you specify a START
WITH
value but omit the NEXT
value, then the database refreshes the materialized view only once. If you omit both the START
WITH
and NEXT
values, or if you omit the create_mv_refresh
entirely, then the database does not automatically refresh the materialized view.
Specify WITH PRIMARY
KEY
to create a primary key materialized view. This is the default and should be used in all cases except those described for WITH
ROWID
. Primary key materialized views allow materialized view master tables to be reorganized without affecting the eligibility of the materialized view for fast refresh. The master table must contain an enabled primary key constraint, and the defining query of the materialized view must specify all of the primary key columns directly. In the defining query, the primary key columns cannot be specified as the argument to a function such as UPPER
.
Restriction on Primary Key Materialized Views You cannot specify this clause for an object materialized view. Oracle Database implicitly refreshes objects materialized WITH
OBJECT
ID
.
See Also:
Oracle Database Advanced Replication for detailed information about primary key materialized views and "Creating Primary Key Materialized Views: Example"Specify WITH
ROWID
to create a rowid materialized view. Rowid materialized views are useful if the materialized view does not include all primary key columns of the master tables. Rowid materialized views must be based on a single table and cannot contain any of the following:
Distinct or aggregate functions
GROUP
BY
or
CONNECT
BY
clauses
Subqueries
Joins
Set operations
The WITH
ROWID
clause has no effect if there are multiple master tables in the defining query.
Rowid materialized views are not eligible for fast refresh after a master table reorganization until a complete refresh has been performed.
Restriction on Rowid Materialized Views You cannot specify this clause for an object materialized view. Oracle Database implicitly refreshes objects materialized WITH
OBJECT
ID
.
See Also:
"Creating Materialized Aggregate Views: Example" and "Creating Rowid Materialized Views: Example"This clause is not valid if your database is in automatic undo mode, because in that mode Oracle Database uses undo tablespaces instead of rollback segments. Oracle strongly recommends that you use automatic undo mode. This clause is supported for backward compatibility with replication environments containing older versions of Oracle Database that still use rollback segments.
For rollback_segment
, specify the remote rollback segment to be used during materialized view refresh.
DEFAULT DEFAULT
specifies that Oracle Database will choose automatically which rollback segment to use. If you specify DEFAULT
, then you cannot specify rollback_segment
. DEFAULT
is most useful when modifying, rather than creating, a materialized view.
See Also:
ALTER MATERIALIZED VIEWMASTER MASTER
specifies the remote rollback segment to be used at the remote master site for the individual materialized view.
LOCAL LOCAL
specifies the remote rollback segment to be used for the local refresh group that contains the materialized view. This is the default.
See Also:
Oracle Database Advanced Replication for information on specifying the local materialized view rollback segment using theDBMS_REFRESH
packageIf you omit rollback_segment
, then the database automatically chooses the rollback segment to be used. One master rollback segment is stored for each materialized view and is validated during materialized view creation and refresh. If the materialized view is complex, then the database ignores any master rollback segment you specify.
The USING
... CONSTRAINTS
clause lets Oracle Database choose more rewrite options during the refresh operation, resulting in more efficient refresh execution. The clause lets Oracle Database use unenforced constraints, such as dimension relationships or constraints in the RELY
state, rather than relying only on enforced constraints during the refresh operation.
The USING
TRUSTED
CONSTRAINTS
clause enables you to create a materialized view on top of a table that has a non-NULL Virtual Private Database (VPD) policy on it. In this case, ensure that the materialized view behaves correctly. Materialized view results are computed based on the rows and columns filtered by VPD policy. Therefore, you must coordinate the materialized view definition with the VPD policy to ensure the correct results. Without the USING
TRUSTED
CONSTRAINTS
clause, any VPD policy on a master table will prevent a materialized view from being created.
Caution:
TheUSING
TRUSTED
CONSTRAINTS
clause lets Oracle Database use dimension and constraint information that has been declared trustworthy by the database administrator but that has not been validated by the database. If the dimension and constraint information is valid, then performance may improve. However, if this information is invalid, then the refresh procedure may corrupt the materialized view even though it returns a success status.If you omit this clause, then the default is USING
ENFORCED
CONSTRAINTS.
Specify NEVER
REFRESH
to prevent the materialized view from being refreshed with any Oracle Database refresh mechanism or packaged procedure. Oracle Database will ignore any REFRESH
statement on the materialized view issued from such a procedure. To reverse this clause, you must issue an ALTER
MATERIALIZED
VIEW
... REFRESH
statement.
Specify FOR
UPDATE
to allow a subquery, primary key, object, or rowid materialized view to be updated. When used in conjunction with Advanced Replication, these updates will be propagated to the master.
The QUERY
REWRITE
clause lets you specify whether the materialized view is eligible to be used for query rewrite.
ENABLE Clause Specify ENABLE
to enable the materialized view for query rewrite.
Restrictions on Enabling Query Rewrite Enabling of query rewrite is subject to the following restrictions:
You can enable query rewrite only if all user-defined functions in the materialized view are DETERMINISTIC
.
You can enable query rewrite only if expressions in the statement are repeatable. For example, you cannot include CURRENT_TIME
or USER
, sequence values (such as the CURRVAL
or NEXTVAL
pseudocolumns), or the SAMPLE
clause (which may sample different rows as the contents of the materialized view change).
Notes:
Query rewrite is disabled by default, so you must specify this clause to make materialized views eligible for query rewrite.
After you create the materialized view, you must collect statistics on it using the DBMS_STATS
package. Oracle Database needs the statistics generated by this package to optimize query rewrite.
See Also:
Oracle Database Data Warehousing Guide for more information on query rewrite
Oracle Database PL/SQL Packages and Types Reference for information about the DBMS_STATS
package
The EXPLAIN_MVIEW
procedure of the DBMS_MVIEW
package for help diagnosing problems with query rewrite and the TUNE_MVIEW
procedure of the DBMS_MVIEW
package correction of query rewrite problems
DISABLE Clause Specify DISABLE
to indicate that the materialized view is not eligible for use by query rewrite. A disabled materialized view can be refreshed.
Specify the defining query of the materialized view. When you create the materialized view, Oracle Database executes this subquery and places the results in the materialized view. This subquery is any valid SQL subquery. However, not all subqueries are fast refreshable, nor are all subqueries eligible for query rewrite.
Notes on the Defining Query of a Materialized View The following notes apply to materialized views:
Oracle Database does not execute the defining query immediately if you specify BUILD
DEFERRED
.
Oracle recommends that you qualify each table and view in the FROM
clause of the defining query of the materialized view with the schema containing it.
Restrictions on the Defining Query of a Materialized View The materialized view query is subject to the following restrictions:
The defining query of a materialized view can select from tables, views, or materialized views owned by the user SYS
, but you cannot enable QUERY
REWRITE
on such a materialized view.
You cannot define a materialized view with a subquery in the select list of the defining query. You can, however, include subqueries elsewhere in the defining query, such as in the WHERE
clause.
Materialized join views and materialized aggregate views with a GROUP
BY
clause cannot select from an index-organized table.
Materialized views cannot contain columns of data type LONG
.
Materialized views cannot contain virtual columns.
You cannot create a materialized view log on a temporary table. Therefore, if the defining query references a temporary table, then this materialized view will not be eligible for FAST
refresh, nor can you specify the QUERY
REWRITE
clause in this statement.
If the FROM
clause of the defining query references another materialized view, then you must always refresh the materialized view referenced in the defining query before refreshing the materialized view you are creating in this statement.
Materialized views with join expressions in the defining query cannot have XML data type columns. The XML data types include XMLType
and URI data type columns.
If you are creating a materialized view enabled for query rewrite, then:
The defining query cannot contain, either directly or through a view, references to ROWNUM
, USER
, SYSDATE
, remote tables, sequences, or PL/SQL functions that write or read database or package state.
Neither the materialized view nor the master tables of the materialized view can be remote.
If you want the materialized view to be eligible for fast refresh using a materialized view log, then some additional restrictions may apply.
See Also:
Oracle Database Data Warehousing Guide for more information on restrictions relating to data warehousing
Oracle Database Advanced Replication for more information on restrictions relating to replication
"Creating Materialized Join Views: Example", "Creating Subquery Materialized Views: Example", and "Creating a Nested Materialized View: Example"
The following examples require the materialized logs that are created in the "Examples" section of CREATE MATERIALIZED VIEW LOG.
Creating a Simple Materialized View: Example The following statement creates a very simple materialized view based on the employees
and table in the hr
schema:
CREATE MATERIALIZED VIEW mv1 AS SELECT * FROM hr.employees;
By default, Oracle Database creates a primary key materialized view with refresh on demand only. If a materialized view log exists on employees
, then mv1
can be altered to be capable of fast refresh. If no such log exists, then only full refresh of mv1
is possible. Oracle Database uses default storage properties for mv1
. The only privileges required for this operation are the CREATE
MATERIALIZED
VIEW
system privilege, and the SELECT
object privilege on hr.employees.
Creating Subquery Materialized Views: Example The following statement creates a subquery materialized view based on the customers
and countries
tables in the sh
schema at the remote
database:
CREATE MATERIALIZED VIEW foreign_customers FOR UPDATE AS SELECT * FROM sh.customers@remote cu WHERE EXISTS (SELECT * FROM sh.countries@remote co WHERE co.country_id = cu.country_id);
Creating Materialized Aggregate Views: Example The following statement creates and populates a materialized aggregate view on the sample sh.sales
table and specifies the default refresh method, mode, and time. It uses the materialized view log created in "Creating a Materialized View Log: Examples", as well as the two additional logs shown here:
CREATE MATERIALIZED VIEW LOG ON times WITH ROWID, SEQUENCE (time_id, calendar_year) INCLUDING NEW VALUES; CREATE MATERIALIZED VIEW LOG ON products WITH ROWID, SEQUENCE (prod_id) INCLUDING NEW VALUES; CREATE MATERIALIZED VIEW sales_mv BUILD IMMEDIATE REFRESH FAST ON COMMIT AS SELECT t.calendar_year, p.prod_id, SUM(s.amount_sold) AS sum_sales FROM times t, products p, sales s WHERE t.time_id = s.time_id AND p.prod_id = s.prod_id GROUP BY t.calendar_year, p.prod_id;
Creating Materialized Join Views: Example The following statement creates and populates the materialized aggregate view sales_by_month_by_state
using tables in the sample sh
schema. The materialized view will be populated with data as soon as the statement executes successfully. By default, subsequent refreshes will be accomplished by reexecuting the defining query of the materialized view:
CREATE MATERIALIZED VIEW sales_by_month_by_state TABLESPACE example PARALLEL 4 BUILD IMMEDIATE REFRESH COMPLETE ENABLE QUERY REWRITE AS SELECT t.calendar_month_desc, c.cust_state_province, SUM(s.amount_sold) AS sum_sales FROM times t, sales s, customers c WHERE s.time_id = t.time_id AND s.cust_id = c.cust_id GROUP BY t.calendar_month_desc, c.cust_state_province;
Creating Prebuilt Materialized Views: Example The following statement creates a materialized aggregate view for the preexisting summary table, sales_sum_table
:
CREATE TABLE sales_sum_table (month VARCHAR2(8), state VARCHAR2(40), sales NUMBER(10,2)); CREATE MATERIALIZED VIEW sales_sum_table ON PREBUILT TABLE WITH REDUCED PRECISION ENABLE QUERY REWRITE 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;
In the preceding example, the materialized view has the same name and also has the same number of columns with the same data types as the prebuilt table. The WITH
REDUCED
PRECISION
clause allows for differences between the precision of the materialized view columns and the precision of the values returned by the subquery.
Creating Primary Key Materialized Views: Example The following statement creates the primary key materialized view catalog
on the sample table oe.product_information
:
CREATE MATERIALIZED VIEW catalog REFRESH FAST START WITH SYSDATE NEXT SYSDATE + 1/4096 WITH PRIMARY KEY AS SELECT * FROM product_information;
Creating Rowid Materialized Views: Example The following statement creates a rowid materialized view on the sample table oe.orders
:
CREATE MATERIALIZED VIEW order_data REFRESH WITH ROWID AS SELECT * FROM orders;
Periodic Refresh of Materialized Views: Example The following statement creates the primary key materialized view emp_data
and populates it with data from the sample table hr.employees
:
CREATE MATERIALIZED VIEW LOG ON employees WITH PRIMARY KEY INCLUDING NEW VALUES; CREATE MATERIALIZED VIEW emp_data PCTFREE 5 PCTUSED 60 TABLESPACE example STORAGE (INITIAL 50K) REFRESH FAST NEXT sysdate + 7 AS SELECT * FROM employees;
The preceding statement does not include a START
WITH
parameter, so Oracle Database determines the first automatic refresh time by evaluating the NEXT
value using the current SYSDATE
. A materialized view log was created for the employee table, so Oracle Database performs a fast refresh of the materialized view every 7 days, beginning 7 days after the materialized view is created.
Because the materialized view conforms to the conditions for fast refresh, the database will perform a fast refresh. The preceding statement also establishes storage characteristics that the database uses to maintain the materialized view.
Automatic Refresh Times for Materialized Views: Example The following statement creates the complex materialized view all_customers
that queries the employee tables on the remote
and local
databases:
CREATE MATERIALIZED VIEW all_customers PCTFREE 5 PCTUSED 60 TABLESPACE example STORAGE (INITIAL 50K) USING INDEX STORAGE (INITIAL 25K) REFRESH START WITH ROUND(SYSDATE + 1) + 11/24 NEXT NEXT_DAY(TRUNC(SYSDATE), 'MONDAY') + 15/24 AS SELECT * FROM sh.customers@remote UNION SELECT * FROM sh.customers@local;
Oracle Database automatically refreshes this materialized view tomorrow at 11:00 a.m. and subsequently every Monday at 3:00 p.m. The default refresh method is FORCE
. The defining query contains a UNION
operator, which is not supported for fast refresh, so the database will automatically perform a complete refresh.
The preceding statement also establishes storage characteristics for both the materialized view and the index that the database uses to maintain it:
The first STORAGE
clause establishes the sizes of the first and second extents of the materialized view as 50 kilobytes each.
The second STORAGE
clause, appearing with the USING
INDEX
clause, establishes the sizes of the first and second extents of the index as 25 kilobytes each.
Creating a Fast Refreshable Materialized View: Example The following statement creates a fast-refreshable materialized view that selects columns from the order_items
table in the sample oe
schema, using the UNION
set operator to restrict the rows returned from the product_information
and inventories
tables using WHERE
conditions. The materialized view logs for order_items
and product_information
were created in the "Examples" section of CREATE
MATERIALIZED
VIEW
LOG
. This example also requires a materialized view log on oe.inventories
.
CREATE MATERIALIZED VIEW LOG ON inventories WITH (quantity_on_hand); CREATE MATERIALIZED VIEW warranty_orders REFRESH FAST AS SELECT order_id, line_item_id, product_id FROM order_items o WHERE EXISTS (SELECT * FROM inventories i WHERE o.product_id = i.product_id AND i.quantity_on_hand IS NOT NULL) UNION SELECT order_id, line_item_id, product_id FROM order_items WHERE quantity > 5;
The materialized view warranty_orders
requires that materialized view logs be defined on order_items
(with product_id
as a join column) and on inventories (with quantity_on_hand
as a filter column). See "Specifying Filter Columns for Materialized View Logs: Example" and "Specifying Join Columns for Materialized View Logs: Example".
Creating a Nested Materialized View: Example The following example uses the materialized view from the preceding example as a master table to create a materialized view tailored for a particular sales representative in the sample oe
schema:
CREATE MATERIALIZED VIEW my_warranty_orders AS SELECT w.order_id, w.line_item_id, o.order_date FROM warranty_orders w, orders o WHERE o.order_id = o.order_id AND o.sales_rep_id = 165;