CREATE MATERIALIZED VIEW

Purpose

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 are called master tables (a replication term) or detail tables (a data warehouse term). This reference uses "master tables" for consistency. The databases containing the master tables are called the master databases.

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.

For 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.

Additional Topics

• Prerequisites
• Syntax
• Semantics
• Examples

Prerequisites

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:

• The owner of the master tables must have the QUERY REWRITE system privilege.
• If you are not the owner of the master tables, you must have the GLOBAL QUERY REWRITE system privilege or the QUERY REWRITE object privilege on each table outside your schema.
• 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), 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 materialized view's master table and index or must have the UNLIMITED TABLESPACE system privilege.

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

Syntax

create_materialized_view::=

Text description of create_materialized_view

(scoped_table_ref_constraint::=, index_org_table_clause::=, materialized_view_props::=, physical_attributes_clause::=, create_mv_refresh::=, subquery::=)

physical_properties::=

Text description of physical_properties

(segment_attributes_clause::=, data_segment_compression::=)

materialized_view_props::=

Text description of materialized_view_props

(column_properties::=, table_partitioning_clauses--part of CREATE TABLE syntax, parallel_clause::=, build_clause::=)

scoped_table_ref_constraint::=

Text description of scoped_table_ref_constraint

index_org_table_clause::=

Text description of index_org_table_clause

(mapping_table_clause: not supported with materialized views, key_compression::=, index_org_overflow_clause::=)

key_compression::=

Text description of key_compression

index_org_overflow_clause::=

Text description of index_org_overflow_clause

(segment_attributes_clause::=)

create_mv_refresh::=

Text description of create_mv_refresh

segment_attributes_clause::=

Text description of segment_attributes_clause

(physical_attributes_clause::=, logging_clause::=)

physical_attributes_clause::=

Text description of physical_attributes_clause

(logging_clause::=)

logging_clause::=

Text description of logging_clause

data_segment_compression::=

Text description of data_segment_compression

column_properties::=

Text description of column_properties

(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)

object_type_col_properties::=

Text description of object_type_col_properties

(substitutable_column_clause::=)

substitutable_column_clause::=

Text description of substitutable_column_clause

nested_table_col_properties::=

Text description of nested_table_col_properties

(substitutable_column_clause::=, object_properties::=, physical_properties::=--part of CREATE TABLE syntax, column_properties::=)

varray_col_properties::=

Text description of varray_col_properties

(substitutable_column_clause::=, LOB_parameters::=)

LOB_storage_clause::=

Text description of LOB_storage_clause

(LOB_parameters::=)

LOB_parameters::=

Text description of LOB_parameters

(storage_clause::=, logging_clause::=)

LOB_partition_storage::=

Text description of LOB_partition_storage

(LOB_storage_clause::=, varray_col_properties::=)

parallel_clause::=

Text description of parallel_clause

build_clause::=

Text description of build_clause

Semantics

schema

Specify the schema to contain the materialized view. If you omit schema, Oracle creates the materialized view in your schema.

materialized_view

Specify the name of the materialized view to be created. Oracle generates names for the table and indexes used to maintain the materialized view by adding a prefix or suffix to the materialized view name.

OF object_type

The OF type_name clause lets you explicitly create an object materialized view of type object_type.

scoped_table_ref_constraint

Use the SCOPE FOR clause to restrict the scope of references to a single table, scope_table_name. The values in the REF column or attribute point to objects in scope_table_name, in which object instances (of the same type as the REF column) are stored.

ON PREBUILT TABLE Clause

The ON PREBUILT TABLE clause lets you register an existing table as a preinitialized materialized view. This 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, the preexisting table reverts to its identity as a table.

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 prebuilt_table_clause

• Each column alias in subquery must correspond to a column in table_name, and corresponding columns must have matching datatypes.
• If you specify this clause, you cannot specify a NOT NULL constraint for any column that is unmanaged (that is, not referenced in subquery) unless you also specify a default value for that column.

  See Also: "Creating Prebuilt Materialized Views: Example"

physical_properties_clause

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.

segment_attributes_clause

Use the segment_attributes_clause to establish values for the PCTFREE, PCTUSED, INITRANS, and MAXTRANS parameters (or, when used in the USING INDEX clause, for the INITRANS and MAXTRANS parameters only), the storage characteristics for the materialized view, to assign a tablespace, and to specify whether logging is to occur.

TABLESPACE Clause

Specify the tablespace in which the materialized view is to be created. If you omit this clause, Oracle creates the materialized view in the default tablespace of the schema containing the materialized view.

logging_clause

Specify LOGGING or NOLOGGING to establish the logging characteristics for the materialized view. The default is the logging characteristic of the tablespace in which the materialized view resides.

data_segment_compression

Use the data_segment_compression clause to instruct Oracle whether to compress data segments to reduce disk and memory use. The COMPRESS keyword enables data segment compression. The NOCOMPRESS keyword disables data segment compression.

index_org_table_clause

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 based 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

• 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.

CLUSTER Clause

The ORGANIZATION CLUSTER clause lets you create the materialized view as part of the specified cluster. A clustered materialized view uses the cluster's space allocation. Therefore, you do not specify physical attributes or the TABLESPACE clause with the CLUSTER clause.

Restriction on clustered materialized views

If you specify ORGANIZATION CLUSTER, you cannot specify the table_partitioning_clauses (in materialized_view_props).

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.

column_properties

The column_properties clause lets you specify the storage characteristics of a LOB, nested table, varray, or XMLType column.

Restriction on Materialized View Columns

The object_type_col_properties are not relevant for a materialized view.

table_partitioning_clauses

The 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.

CACHE | NOCACHE

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.

parallel_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.

NOPARALLEL

Specify NOPARALLEL for serial execution. This is the default.

PARALLEL

Specify PARALLEL if you want Oracle to select a degree of parallelism equal to the number of CPUs available on all participating instances times the value of the PARALLEL_THREADS_PER_CPU initialization parameter.

PARALLEL integer

Specification of integer indicates the degree of parallelism, which is the number of parallel threads used in the parallel operation. Each parallel thread may use one or two parallel execution servers. Normally Oracle calculates the optimum degree of parallelism, so it is not necessary for you to specify integer.

build_clause

The build_clause lets you specify when to populate the materialized view.

IMMEDIATE

Specify IMMEDIATE to indicate that the materialized view is populated immediately. This is the default.

DEFERRED

Specify DEFERRED to indicate that the materialized view will 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.

USING INDEX Clause

The USING INDEX clause lets you establish the value of INITRANS, MAXTRANS, and STORAGE parameters for the default index Oracle uses to maintain the materialized view's data. If USING INDEX is not specified, then default values are used for the index. Oracle 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.

USING NO INDEX 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).

create_mv_refresh

Use the create_mv_refresh to specify the default methods, modes, and times for Oracle to refresh the materialized view. If the master tables of a materialized view are modified, 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 Oracle to refresh the materialized view.

FAST Clause

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 are stored either in the materialized view log associated with the master table (for conventional DML changes) or in the direct loader log (for direct-path INSERT operations).

If you specify REFRESH FAST, the CREATE statement will fail unless materialized view logs already exist for the materialized view's master tables. (Oracle 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 subquery contains an analytic function.

COMPLETE Clause

Specify COMPLETE to indicate the complete refresh method, which is implemented by executing the materialized view's defining subquery. If you request a complete refresh, Oracle performs a complete refresh even if a fast refresh is possible.

FORCE Clause

Specify FORCE to indicate that when a refresh occurs, Oracle will perform a fast refresh if one is possible or a complete refresh otherwise. If you do not specify a refresh method (FAST, COMPLETE, or FORCE), FORCE is the default.

ON COMMIT Clause

Specify ON COMMIT to indicate that a fast refresh is to occur whenever Oracle 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 Oracle performs the refresh operation as part of the commit process.

Restriction on Refreshing ON COMMIT

This clause is not supported for materialized views containing object types.

ON DEMAND Clause

Specify ON DEMAND to indicate that the materialized view will 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.

If you specify ON COMMIT or ON DEMAND, you cannot also specify START WITH or NEXT.

START WITH Clause

Specify a date expression for the first automatic refresh time.

NEXT Clause

Specify a date 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, Oracle 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, Oracle 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, Oracle does not automatically refresh the materialized view.

WITH PRIMARY KEY Clause

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.

Restriction on Primary Key Materialized Views

You cannot specify this clause for an object materialized view. Oracle implicitly refreshes object materialized WITH OBJECT ID.

WITH ROWID Clause

Specify WITH ROWID to create a rowid materialized view. Rowid materialized views provide compatibility with master tables in releases of Oracle prior to 8.0.

You can also use rowid materialized views 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

Rowid materialized views are not eligible for fast refreshed 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 implicitly refreshes object materialized WITH OBJECT ID.

USING ROLLBACK SEGMENT Clause

Specify the remote rollback segment to be used during materialized view refresh, where rollback_segment is the name of the rollback segment to be used.

This clause is invalid if your database is in Automatic Undo Mode, because in that mode Oracle uses undo tablespaces instead of rollback segments.

DEFAULT

DEFAULT specifies that Oracle will choose automatically which rollback segment to use. If you specify DEFAULT, you cannot specify rollback_segment.

DEFAULT is most useful when modifying (rather than creating) a materialized view.

MASTER

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.

If you do not specify MASTER or LOCAL, Oracle uses LOCAL by default. If you do not specify rollback_segment, Oracle 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, the master rollback segment, if specified, is ignored.

NEVER REFRESH Clause

Specify NEVER REFRESH to prevent the materialized view from being refreshed with any Oracle refresh mechanism or packaged procedure. Oracle 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.

FOR UPDATE Clause

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.

QUERY REWRITE Clause

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

• 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. Be sure to analyze the materialized view after you create it. Oracle needs the statistics generated by the ANALYZE operation to optimize query rewrite.

  See Also: Oracle9i Data Warehousing Guide for more information on query rewrite CREATE FUNCTION

DISABLE Clause

Specify DISABLE to indicate that the materialized view is not eligible for use by query rewrite. However, a disabled materialized view can be refreshed.

AS subquery

Specify the defining subquery of the materialized view. When you create the materialized view, Oracle executes this subquery and places the results in the materialized view. This subquery is any valid SQL subquery. However, not all queries are fast refreshable, nor are all subqueries eligible for query rewrite.

Notes on the Defining Query of a Materialized View

• Oracle does not execute the defining subquery immediately if you specify BUILD DEFERRED.
• Oracle recommends that you qualify each table and view in the FROM clause of the defining subquery of the materialized view with the schema containing it.

  See Also: "AS subquery" clause of CREATE TABLE for some additional caveats

Restrictions on the Defining Subquery of a Materialized View

• The defining subquery 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.
• 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 datatype LONG.
• You cannot create a materialized view log on a temporary table. Therefore, if the defining subquery references a temporary table, 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 subquery references another materialized view, then you must always refresh the materialized view referenced in the defining subquery before refreshing the materialized view you are creating in this statement.

If you are creating a materialized view enabled for query rewrite:

• The defining subquery 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, some additional restrictions may apply.

Examples

The following examples require the materialized logs that are created in the "Examples" section of CREATE MATERIALIZED VIEW.

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 materialized view's query:

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 this example, the materialized view has the same name as the prebuilt table and also has the same number of columns with the same datatypes as the prebuilt table. The WITH REDUCED PRECISION clause allows for between the precision of the materialized view columns and the precision of the values returned by the subquery.

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 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 NEXT 50K)
   REFRESH FAST NEXT sysdate + 7 
   AS SELECT * FROM employees; 

The statement does not include a START WITH parameter, so Oracle 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 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, Oracle will perform a fast refresh. The preceding statement also establishes storage characteristics that Oracle 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 NEXT 50K) 
   USING INDEX STORAGE (INITIAL 25K NEXT 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 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. all_emps contains a UNION operator, which is not supported for fast refresh, so Oracle will automatically perform a complete refresh.

The preceding statement also establishes storage characteristics for both the materialized view and the index that Oracle uses to maintain it:

• The first establishes the sizes of the first and second extents of the materialized view as 50 kilobytes each.
• The second (appearing with the USING INDEX clause) establishes the sizes of the first and second extents of the index as 25 kilobytes each.

Specifying Rollback Segments for Materialized Views: Example

The following statement creates the primary key materialized view sales_emp with rollback segment master_seg at the remote master and rollback segment snap_seg for the local refresh group that contains the materialized view.

CREATE MATERIALIZED VIEW sales_emp 
   REFRESH FAST START WITH SYSDATE NEXT SYSDATE + 7
   USING MASTER ROLLBACK SEGMENT master_seg 
   LOCAL ROLLBACK SEGMENT snap_seg  
   AS SELECT * FROM bar;  

The following statement is incorrect and generates an error because it specifies a segment name with a DEFAULT rollback segment:

/* The following statement is invalid. */
CREATE MATERIALIZED VIEW order_mv 
   REFRESH FAST START WITH SYSDATE NEXT SYSDATE + 7
   USING DEFAULT ROLLBACK SEGMENT mv_seg 
   AS SELECT * FROM orders; 

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 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; 

This materialized view 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;