Create Indexed Views

This topic describes how to create an indexed view in SQL Server 2012 by using Transact-SQL. The first index created on a view must be a unique clustered index. After the unique clustered index has been created, you can create nonclustered indexes. Creating a unique clustered index on a view improves query performance because the view is stored in the database in the same way a table with a clustered index is stored. The query optimizer may use indexed views to speed up the query execution. The view does not have to be referenced in the query for the optimizer to consider that view for a substitution.

In This Topic

• Before you begin:

  Limitations and Restrictions

  Recommendations

  Considerations

  Security

• To create an indexed view, using:

  Transact-SQL

Before You Begin

The following steps are required to create an indexed view and are critical to the successful implementation of the indexed view:

1. Verify the SET options are correct for all existing tables that will be referenced in the view.

2. Verify that the SET options for the session are set correctly before creating any new tables and the view.

3. Verify that the view definition is deterministic.

4. Create the view by using the WITH SCHEMABINDING option.

5. Create the unique clustered index on the view.

Required SET Options for Indexed Views

Evaluating the same expression can produce different results in the Database Engine when different SET options are active when the query is executed. For example, after the SET option CONCAT_NULL_YIELDS_NULL is set to ON, the expression 'abc' + NULL returns the value NULL. However, after CONCAT_NULL_YIEDS_NULL is set to OFF, the same expression produces 'abc'.

To make sure that the views can be maintained correctly and return consistent results, indexed views require fixed values for several SET options. The SET options in the following table must be set to the values shown in the Required Value column whenever the following conditions occur:

• The view and subsequent indexes on the view are created.

• The base tables referenced in the view at the time the table is created.

• There is any insert, update, or delete operation performed on any table that participates in the indexed view. This requirement includes operations such as bulk copy, replication, and distributed queries.

• The indexed view is used by the query optimizer to produce the query plan.

  SET options	Required value	Default server value	Default OLE DB and ODBC value	Default DB-Library value
  ANSI_NULLS	ON	ON	ON	OFF
  ANSI_PADDING	ON	ON	ON	OFF
  ANSI_WARNINGS*	ON	ON	ON	OFF
  ARITHABORT	ON	ON	OFF	OFF
  CONCAT_NULL_YIELDS_NULL	ON	ON	ON	OFF
  NUMERIC_ROUNDABORT	OFF	OFF	OFF	OFF
  QUOTED_IDENTIFIER	ON	ON	ON	OFF

  *Setting ANSI_WARNINGS to ON implicitly sets ARITHABORT to ON when the database compatibility level is set to 90 or higher.

If you are using an OLE DB or ODBC server connection, the only value that must be modified is the ARITHABORT setting. All DB-Library values must be set correctly either at the server level by using sp_configure or from the application by using the SET command.

Ważne:
We strongly recommend that you set the ARITHABORT user option to ON server-wide as soon as the first indexed view or index on a computed column is created in any database on the server.

Deterministic Views

The definition of an indexed view must be deterministic. A view is deterministic if all expressions in the select list, as well as the WHERE and GROUP BY clauses, are deterministic. Deterministic expressions always return the same result any time they are evaluated with a specific set of input values. Only deterministic functions can participate in deterministic expressions. For example, the DATEADD function is deterministic because it always returns the same result for any given set of argument values for its three parameters. GETDATE is not deterministic because it is always invoked with the same argument, but the value it returns changes each time it is executed.

To determine whether a view column is deterministic, use the IsDeterministic property of the COLUMNPROPERTY function. To determine if a deterministic column in a view with schema binding is precise, use the IsPrecise property of the COLUMNPROPERTY function COLUMNPROPERTY returns 1 if TRUE, 0 if FALSE, and NULL for input that is not valid. This means that the column is not deterministic or not precise.

Even if an expression is deterministic, if it contains float expressions, the exact result may depend on the processor architecture or version of microcode. To ensure data integrity, such expressions can participate only as nonkey columns of indexed views. Deterministic expressions that do not contain float expressions are called precise. Only precise deterministic expressions can participate in key columns and in WHERE or GROUP BY clauses of indexed views.

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Additional Requirements

In addition to the SET options and deterministic function requirements, the following requirements must be met:

• The user that executes CREATE INDEX must be the owner of the view.

• When you create the index, the IGNORE_DUP_KEY option must be set to OFF (the default setting).

• Tables must be referenced by two-part names, schema**.**tablename in the view definition.

• User-defined functions referenced in the view must be created by using the WITH SCHEMABINDING option.

• Any user-defined functions referenced in the view must be referenced by two-part names, schema**.**function.

• The data access property of a user-defined function must be NO SQL, and external access property must be NO.

• Common language runtime (CLR) functions can appear in the select list of the view, but cannot be part of the definition of the clustered index key. CLR functions cannot appear in the WHERE clause of the view or the ON clause of a JOIN operation in the view.

• CLR functions and methods of CLR user-defined types used in the view definition must have the properties set as shown in the following table.

  Property	Note
  DETERMINISTIC = TRUE	Must be declared explicitly as an attribute of the Microsoft .NET Framework method.
  PRECISE = TRUE	Must be declared explicitly as an attribute of the .NET Framework method.
  DATA ACCESS = NO SQL	Determined by setting DataAccess attribute to DataAccessKind.None and SystemDataAccess attribute to SystemDataAccessKind.None.
  EXTERNAL ACCESS = NO	This property defaults to NO for CLR routines.

• The view must be created by using the WITH SCHEMABINDING option.

• The view must reference only base tables that are in the same database as the view. The view cannot reference other views.

• The SELECT statement in the view definition must not contain the following Transact-SQL elements:

  COUNT	ROWSET functions (OPENDATASOURCE, OPENQUERY, OPENROWSET, AND OPENXML)	OUTER joins (LEFT, RIGHT, or FULL)
  Derived table (defined by specifying a SELECT statement in the FROM clause)	Self-joins	Specifying columns by using SELECT * or SELECT table_name.*
  DISTINCT	STDEV, STDEVP, VAR, VARP, or AVG	Common table expression (CTE)
  float*, text, ntext, image, XML, or filestream columns	Subquery	OVER clause, which includes ranking or aggregate window functions
  Full-text predicates (CONTAIN, FREETEXT)	SUM function that references a nullable expression	ORDER BY
  CLR user-defined aggregate function	TOP	CUBE, ROLLUP, or GROUPING SETS operators
  MIN, MAX	UNION, EXCEPT, or INTERSECT operators	TABLESAMPLE
  Table variables	OUTER APPLY or CROSS APPLY	PIVOT, UNPIVOT
  Sparse column sets	Inline or multi-statement table-valued functions	OFFSET
  CHECKSUM_AGG

  *The indexed view can contain float columns; however, such columns cannot be included in the clustered index key.

• If GROUP BY is present, the VIEW definition must contain COUNT_BIG(*) and must not contain HAVING. These GROUP BY restrictions are applicable only to the indexed view definition. A query can use an indexed view in its execution plan even if it does not satisfy these GROUP BY restrictions.

• If the view definition contains a GROUP BY clause, the key of the unique clustered index can reference only the columns specified in the GROUP BY clause.

Recommendations

When you refer to datetime and smalldatetime string literals in indexed views, we recommend that you explicitly convert the literal to the date type you want by using a deterministic date format style. For a list of the date format styles that are deterministic, see CAST and CONVERT (Transact-SQL). Expressions that involve implicit conversion of character strings to datetime or smalldatetime are considered nondeterministic. This is because the results depend on the LANGUAGE and DATEFORMAT settings of the server session. For example, the results of the expression CONVERT (datetime, '30 listopad 1996', 113) depend on the LANGUAGE setting because the string 'listopad' means different months in different languages. Similarly, in the expression DATEADD(mm,3,'2000-12-01'), SQL Server interprets the string '2000-12-01' based on the DATEFORMAT setting.

Implicit conversion of non-Unicode character data between collations is also considered nondeterministic.

Creating indexes on views that contain these implicit conversion expressions is not allowed in compatibility level 90 and higher. However, existing views that contain these expressions from an upgraded database are maintainable. If you use indexed views that contain implicit string to date conversions, be certain that the LANGUAGE and DATEFORMAT settings are consistent in your databases and applications to avoid possible indexed view corruption.

Considerations

The setting of the large_value_types_out_of_row option of columns in an indexed view is inherited from the setting of the corresponding column in the base table. This value is set by using sp_tableoption. The default setting for columns formed from expressions is 0. This means that large value types are stored in-row.

Indexed views can be created on a partitioned table, and can themselves be partitioned.

To prevent the Database Engine from using indexed views, include the OPTION (EXPAND VIEWS) hint on the query. Also, if any of the listed options are incorrectly set, this will prevent the optimizer from using the indexes on the views. For more information about the OPTION (EXPAND VIEWS) hint, see SELECT (Transact-SQL).

All indexes on a view are dropped when the view is dropped. All nonclustered indexes and auto-created statistics on the view are dropped when the clustered index is dropped. User-created statistics on the view are maintained. Nonclustered indexes can be individually dropped. Dropping the clustered index on the view removes the stored result set, and the optimizer returns to processing the view like a standard view.

Indexes on tables and views can be disabled. When a clustered index on a table is disabled, indexes on views associated with the table are also disabled.

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Security

Permissions

Requires CREATE VIEW permission in the database and ALTER permission on the schema in which the view is being created.

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Using Transact-SQL

To create an indexed view

1. In Object Explorer, connect to an instance of Database Engine.

2. On the Standard bar, click New Query.

3. Copy and paste the following example into the query window and click Execute. The example creates a view and an index on that view. Two queries are included that use the indexed view.

   USE AdventureWorks2012;
   GO
   --Set the options to support indexed views.
   SET NUMERIC_ROUNDABORT OFF;
   SET ANSI_PADDING, ANSI_WARNINGS, CONCAT_NULL_YIELDS_NULL, ARITHABORT,
       QUOTED_IDENTIFIER, ANSI_NULLS ON;
   GO
   --Create view with schemabinding.
   IF OBJECT_ID ('Sales.vOrders', 'view') IS NOT NULL
   DROP VIEW Sales.vOrders ;
   GO
   CREATE VIEW Sales.vOrders
   WITH SCHEMABINDING
   AS
       SELECT SUM(UnitPrice*OrderQty*(1.00-UnitPriceDiscount)) AS Revenue,
           OrderDate, ProductID, COUNT_BIG(*) AS COUNT
       FROM Sales.SalesOrderDetail AS od, Sales.SalesOrderHeader AS o
       WHERE od.SalesOrderID = o.SalesOrderID
       GROUP BY OrderDate, ProductID;
   GO
   --Create an index on the view.
   CREATE UNIQUE CLUSTERED INDEX IDX_V1 
       ON Sales.vOrders (OrderDate, ProductID);
   GO
   --This query can use the indexed view even though the view is 
   --not specified in the FROM clause.
   SELECT SUM(UnitPrice*OrderQty*(1.00-UnitPriceDiscount)) AS Rev, 
       OrderDate, ProductID
   FROM Sales.SalesOrderDetail AS od
       JOIN Sales.SalesOrderHeader AS o ON od.SalesOrderID=o.SalesOrderID
           AND ProductID BETWEEN 700 and 800
           AND OrderDate >= CONVERT(datetime,'05/01/2002',101)
   GROUP BY OrderDate, ProductID
   ORDER BY Rev DESC;
   GO
   --This query can use the above indexed view.
   SELECT  OrderDate, SUM(UnitPrice*OrderQty*(1.00-UnitPriceDiscount)) AS Rev
   FROM Sales.SalesOrderDetail AS od
       JOIN Sales.SalesOrderHeader AS o ON od.SalesOrderID=o.SalesOrderID
           AND DATEPART(mm,OrderDate)= 3
           AND DATEPART(yy,OrderDate) = 2002
   GROUP BY OrderDate
   ORDER BY OrderDate ASC;
   GO
   

For more information, see CREATE VIEW (Transact-SQL).

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Zobacz także

Odwołanie

CREATE INDEX (Transact-SQL)

SET ANSI_NULLS (Transact-SQL)

SET ANSI_PADDING (Transact-SQL)

SET ANSI_WARNINGS (Transact-SQL)

SET ARITHABORT (Transact-SQL)

SET CONCAT_NULL_YIELDS_NULL (Transact-SQL)

SET NUMERIC_ROUNDABORT (Transact-SQL)

SET QUOTED_IDENTIFIER (Transact-SQL)