The receiver is responsible for receiving and applying the deferred transactions from the propagator at multitier materialized view sites that are based on the master materialized view. As you will see in the following section, you can rescope a REF column to a local materialized view or table at the materialized view site during creation of the materialized view. Use the CREATE MATERIALIZED VIEW statement to create a materialized view. If the master has a system generated OID, then the OIDs of row objects in the materialized view are system generated. In this case, the CREATE MATERIALIZED VIEW statement that creates the orders materialized view has a subquery with a many to one relationship, because there can be many orders for each customer. A refresh group can contain up to 400 materialized views. If the refresher of a materialized view is not the owner, certain privileges must be granted to the refresher and to the owner. Materialized views do not require a dedicated network connection. If there is a conflict between an updatable materialized view and a master, then, during a refresh, the conflict may result in an entry in the updatable materialized view log that is not in the materialized view log at the master site or master materialized view site. Unlike an ordinary Oracle Database View which does not contain any data, a materialized view is an Oracle Database object that contains the results of a query. Log onto SlightBook to understand more about Materialized View in Oracle along with Oracle … Some reasons to use data subsetting are to: For example, the following statement creates a materialized view based on the oe.orders@orc1.world master table and includes only the rows for the sales representative with a sales_rep_id number of 173: Rows of the orders table with a sales_rep_id number other than 173 are excluded from this materialized view. SELECT object privilege on the master and the master's materialized view log or SELECT ANY TABLE system privilege. To rescope a materialized view, you can either use the SCOPE FOR clause in the CREATE MATERIALIZED VIEW statement, or you can use the ALTER MATERIALIZED VIEW statement after creating the materialized view. Also, PL/SQL only supports dereferencing REFs by using the UTL_OBJECT package and raises an exception for dangling REFs. Further, the ability of multimaster replication to provide real-time or near real-time replication may result in greater network traffic, and might require a dedicated network link. You must have the privileges necessary to create these objects. These are used to copy data to non-master sites, in a duplication domain and to store costly queries in a data storehouse domain. If possible, you should avoid using complex materialized views because they cannot be fast refreshed, which may degrade network performance (see "Refresh Process" for information). You can perform fast refreshes of materialized views only when the master table or master materialized view has a materialized view log. After the required types are created at the materialized view site, you can create an object materialized view by specifying the OF type clause. To replicate schema objects based on user-defined types, the user-defined types themselves must exist, and must be exactly the same, at all replication sites. But, if you want to replicate data based on the information in more than one table, then maintaining and defining these materialized views may be difficult. As you can see, the materialized view created by this statement is fast refreshable and updatable. To keep a materialized view's data relatively current with the data of its master, the materialized view must be refreshed periodically. If the owner of materialized view at the materialized view site has a private database link to the master site or master materialized view site, then the database link connects to the owner of the master at the master site or master materialized view site. However, if you try to refresh orders_lev2, Oracle returns an error because orders_lev1 no longer exists. A read-only materialized view does not create this log, and Oracle does not use this log during a complete refresh because, in this case, the entire materialized view is replaced. It inserts a row into the materialized view log whenever an INSERT, UPDATE, or DELETE statement modifies the table's data. That is, this statement creates a materialized view that contains customers who have an order with an order total greater than $20,000: To create this oe.customers materialized view, customer_id and order_total must be logged in the materialized view log for the orders table. If you do not use the replication management API for these actions, then replication errors may result. If you are creating a materialized view based on a master that has a scoped REF column, then you can rescope the REF to a different object table or object materialized view at the materialized view site. In addition, replicating less data means that there is less activity on the network. They can also be used to precompute joins with or without aggregations. Also, for fast refreshes to be faster than complete refreshes, each join column in the CREATE MATERIALIZED VIEW statement must have an index on it. During the refresh of a refresh group, each materialized view in the group is locked at the materialized view site for the amount of time required to refresh all of the materialized views in the refresh group. Consider a multinational company that maintains all employee information at headquarters, which is in the in the United States. Similarly, if a customer's credit limit drops to less than $10,000, then the customer's data will be removed from the materialized view during the subsequent refresh process. Materialized Views in Oracle; Introduction. A scoped REF is a REF that can contain references only to a specified object table, while an unscoped REF can contain references to any object table in the database that is based on the corresponding object type. A scoped REF requires less storage space and provides more efficient access than an unscoped REF. The company uses the tables in the hr schema to maintain the employee information. Typically, tables that contain column objects also con… Replicating and distributing dataIn large databases, particularly data warehousing environments, there is always a … Here, the replication environment can be configured with the master site at the international headquarters and with materialized views at the national level. When using a group owner, remember that each materialized view object must have a unique name. When you create the inventories materialized view, you want to retrieve the inventories with the quantity on hand greater than zero for the products that appear in the order_items table. Materialized views can be stored in the same database as their base tables or views, or in a separate database. In Figure 3-8, two level 2 materialized views are based on one level 1 materialized view. The following statement uses the UNION operator and subqueries to capture this data in a materialized view for products in category_id 29: To create the oe.product_information materialized view, translated_description in the product_descriptions table and state_province in the locations table must be logged in each master's materialized view log. That is, an object materialized view is composed of row objects, and each row object is identified by an object identifier (OID) column. The following is an example of a SQL statement for creating an updatable, primary key materialized view: Primary key materialized views may contain a subquery so that you can create a subset of rows at the remote materialized view site. You create object types using the CREATE TYPE ... AS OBJECT statement. Multitier materialized views offer greater flexibility in the design of a replication environment. Materialized views also differ from views because they are "redundant", being copied from the base tables. A materialized view is a database object that contains the results of a query. A receiver must be registered at a master materialized view site. To perform a fast refresh, the master that manages the materialized view first identifies the changes that occurred in the master since the most recent refresh of the materialized view and then applies these changes to the materialized view. That is, one customer can have many orders. 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