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Even though both forms of a partitioned view use a UNION ALL statement, you can perform updates to a partitioned view. Partitioned views place additional restrictions on the view definition, as well as any transactions, as outlined in the SQL Server Books Online article CREATE VIEW (Transact-SQL) at http://msdn.microsoft.com/en-us/library/ms187956.aspx.

In addition to making data modifications through a view, you can also create an index on a view. However, an index cannot be created on a partitioned view because the member tables can span databases and SQL Server instances.

When a regular view is created, SQL Server stores only the definition of the view, which is then substituted by the optimizer for SELECT statements issued against the view. An index can be built against a list of values in a column. When you index a view, SQL Server executes the SELECT statement defined by the view, stores the result set, and then builds the index. Any subsequent DML issued against any of the tables the view is defined against causes SQL Server to update the stored result set incrementally, as well as maintain the index, if necessary. Because SQL Server physically stores and maintains the result set, or materializes the data, an indexed view is sometimes referred to as a materialized view. Indexed views have a very long list of requirements. The requirements for an indexed view derive from the fact that the data has to be materialized to disk in an unchanging manner and the data within the index also has to be fixed. Some of the requirements for creating an indexed view are as follows:

The SELECT statement cannot reference other views. All functions must be deterministic. AVG, MIN, MAX, STDEV, STDEVP, VAR, and VARP are not allowed. The index created must be both clustered and unique. ANSI_NULLS must have been set to ON when the view and any tables referenced by the view were created. The view must be created with the SCHEMABINDING option. The SELECT statement must not contain subqueries, outer joins, EXCEPT, INTERSECT, TOP, UNION, ORDER BY, DISTINCT, COMPUTE/COMPUTE BY, CROSS/OUTER APPLY, PIVOT, or UNPIVOT.

The complete list of restrictions for creating an indexed view can be found in the SQL Server Books Online article Creating Indexed Views, at http://msdn.microsoft.com/en-us/ library/ms191432.aspx.

Meeting the requirements for creating an indexed view may seem prohibitive. However, the main advantage of an indexed view is that the data is already materialized and does not have to be calculated on the fly, as with a regular view. Indexed views can provide a significant performance gain when you have queries that combine large volumes of data, such as with aggregates. Indexed views have to be maintained when changes occur to the underlying tables, so an indexed view shouldn t be created against tables that receive large volumes of data modifications.

For the exam, you should understand the requirements to create an indexed view, as well as how an indexed view can improve performance of your applications.

Programming Microsoft SQL Server with T-SQL User-Defined Stored Procedures, Functions, Triggers, and Views

A function that returns the same value every time it is called, given the same input parameters, is a deterministic function. A function that could return a different value each time it is called, given the same input parameters, is a nondeterministic function. An example of a deterministic function is SUBSTRING because it returns the same value every time for the same input parameters. Examples of nondeterministic functions are RAND and GETDATE because each one could return a different value each time it is called. Functions can be used in computed columns, as well as within views. You can also create an index on a computed column as well as indexing a view. To create an index, the results of a function must be deterministic, such that the set of values for the index is fixed. Also, because creating an index on a view causes the results of the view to be materialized and stored, to index a view, every function within the view must be deterministic.