Create indexed views
This article describes how to create indexes on a view. The first index created on a view must be a unique clustered index. After the unique clustered index has been created, you can create more 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 doesn't have to be referenced in the query for the optimizer to consider that view for a substitution.
The following steps are required to create an indexed view and are critical to the successful implementation of the indexed view:
- Verify the
SEToptions are correct for all existing tables that will be referenced in the view.
- Verify that the SET options for the session are set correctly before you create any tables and the view.
- Verify that the view definition is deterministic.
- Verify that the base table has the same owner as the view.
- Create the view by using the
- Create the unique clustered index on the view.
INSERT operations (Data Manipulation Language, or DML) on a table referenced by a large number of indexed views, or fewer but very complex indexed views, those referenced indexed views will have to be updated as well. As a result, DML query performance can degrade significantly, or in some cases, a query plan cannot even be produced.
In such scenarios, test your DML queries before production use, analyze the query plan and tune/simplify the DML statement.
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_YIELDS_NULL is set to OFF, the same expression produces
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 view 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
ANSI_WARNINGS to ON implicitly sets
ARITHABORT to ON.
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
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 view requirement
The definition of an indexed view must be deterministic. A view is deterministic if all expressions in the select list, as well as the
GROUP BY clauses, are deterministic. Deterministic expressions always return the same result anytime 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 isn't 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
NULL for input that isn't valid. This means the column isn't 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 non-key columns of indexed views. Deterministic expressions that don't contain float expressions are called precise. Only precise deterministic expressions can participate in key columns and in
GROUP BY clauses of indexed views.
The following requirements must also be met, in addition to the
SET options and deterministic function requirements
The user that executes
CREATE INDEXmust be the owner of the view.
When you create the index, the
IGNORE_DUP_KEYindex 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
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
Common language runtime (CLR) functions can appear in the select list of the view, but can't be part of the definition of the clustered index key. CLR functions can't 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 the
EXTERNAL ACCESS = NO This property defaults to NO for CLR routines.
The view must be created by using the
The view must reference only base tables that are in the same database as the view. The view can't reference other views.
GROUP BYis present, the VIEW definition must contain
COUNT_BIG(*)and must not contain
GROUP BYrestrictions are applicable only to the indexed view definition. A query can use an indexed view in its execution plan even if it doesn't satisfy these
If the view definition contains a
GROUP BYclause, the key of the unique clustered index can reference only the columns specified in the
The SELECT statement in the view definition must not contain the following Transact-SQL syntax:
Transact-SQL function Possible alternatives
ROWSET functions (
SUMas separate columns
Statistical aggregate functions (
SUMfunction that references a nullable expression
SUM()to make the expression non-nullable
Other aggregate functions (
User-defined aggregate functions (SQL CLR) SELECT clause Transact-SQL element Possible alternative
WITH cte AS
Common table expressions (CTE)
SELECT [ <table>. ] *
Explicitly name columns
OVERclause, which includes ranking or aggregate window functions
LEFT OUTER JOIN
RIGHT OUTER JOIN
FULL OUTER JOIN
Derived table expressions (that is, using
Inline table-valued function
Multi-statement table-valued function
Query the temporal history table directly
Full-text predicates (
Define separate indexed views for each combination of
AND NOT, and
Source column type Possible alternative Deprecated large value column types text, ntext, and image Migrate columns to varchar(max), nvarchar(max), and varbinary(max) respectively. xml or FILESTREAM columns float 1 columns in index key Sparse column sets
1 The indexed view can contain float columns; however, such columns can't be included in the clustered index key.
Indexed views are not supported on top of temporal queries (queries that use
datetime and smalldatetime 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). For more information about deterministic and nondeterministic expressions, see the Considerations section in this page.
Expressions that involve implicit conversion of character strings to datetime or smalldatetime are considered nondeterministic. For more information, see Nondeterministic conversion of literal date strings into DATE values.
Performance considerations with indexed views
When you execute DML (such as
INSERT) on a table referenced by a large number of indexed views, or fewer but complex indexed views, those indexed views will have to be updated as well during DML execution. As a result, DML query performance may degrade significantly, or in some cases, a query plan can't even be produced. In such scenarios, test your DML queries before production use, analyze the query plan and tune/simplify the DML statement.
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).
Various additional 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.
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.
To create the view, a user needs to hold the CREATE VIEW permission in the database and ALTER permission on the schema in which the view is being created. If the base table resides within a different schema, the REFERENCES permission on the table is required as a minimum. If the user creating the index differs from the users who created the view, for the index creation alone the ALTER permission on the view is required (covered by ALTER on the schema).
Indexes can only be created on views that have the same owner as the referenced table or tables. This is also called an intact ownership chain between the view and the table(s). Typically, when table and view reside within the same schema, the same schema owner applies to all objects within the schema. Therefore it's possible to create a view and not be the owner of the view. On the other hand is also possible that individual objects within a schema have different explicit owners. The
principal_id column in
sys.tables contains a value if the owner is different from the schema owner.
Create an indexed view: a T-SQL example
The following example creates a view and an index on that view, in the
--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; --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
The next two queries demonstrate how the indexed view can be used, even though the view isn't specified in the
--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 o.OrderDate >= CONVERT(datetime, '05/01/2012', 101) WHERE od.ProductID BETWEEN 700 and 800 GROUP BY OrderDate, ProductID ORDER BY Rev DESC; GO --This query will also 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 o.OrderDate >= CONVERT(datetime,'03/01/2012', 101) AND o.OrderDate < CONVERT(datetime,'04/01/2012', 101) GROUP BY OrderDate ORDER BY OrderDate ASC;
Finally, this example shows querying directly from the indexed view. On SQL Server Standard edition, you must use the
NOEXPAND query hint to query the indexed view directly.
--This query uses the indexed view directly, on Enterprise edition. SELECT OrderDate, Revenue FROM Sales.vOrders WHERE OrderDate >= CONVERT(datetime,'03/01/2012', 101) AND OrderDate < CONVERT(datetime,'04/01/2012', 101) ORDER BY OrderDate ASC; --This query uses the indexed view directly, with the NOEXPAND hint. SELECT OrderDate, Revenue FROM Sales.vOrders WITH (NOEXPAND) WHERE OrderDate >= CONVERT(datetime,'03/01/2012', 101) AND OrderDate < CONVERT(datetime,'04/01/2012', 101) ORDER BY OrderDate ASC;
For more information, see CREATE VIEW (Transact-SQL).