Create indexed views

Cikk
07/22/2024

Applies to: SQL Server Azure SQL Database Azure SQL Managed Instance

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 can 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.

Steps

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

Verify the SET options 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 WITH SCHEMABINDING option.
Create the unique clustered index on the view.

When you execute UPDATE, DELETE or INSERT operations (Data Manipulation Language, or DML) on a table referenced by a large number of indexed views, or fewer but complex indexed views, those referenced indexed views have to be updated as well. As a result, DML query performance can 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.

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 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 view is created.
When any insert, update, or delete operation is 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` ¹	`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`

¹ Setting ANSI_WARNINGS to ON implicitly sets ARITHABORT to ON.

If you use 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.

Important

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, and the WHERE and GROUP BY clauses, are deterministic. Deterministic expressions always return the same result whenever they're 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's always invoked with the same argument, but the value it returns changes each time it executes.

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 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 depends 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 WHERE or GROUP BY clauses of indexed views.

Additional requirements

The following requirements must also be met, in addition to the SET options and deterministic function requirements

The user that executes CREATE INDEX must be the owner of the view.
When you create the index, the IGNORE_DUP_KEY index 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 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 `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 can't reference other views.
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 doesn't 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.

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

Transact-SQL function	Possible alternatives
`COUNT`	Use `COUNT_BIG`
`ROWSET` functions (`OPENDATASOURCE`, `OPENQUERY`, `OPENROWSET`, and `OPENXML`)
Arithmetic mean (`AVG`)	Use `COUNT_BIG` and `SUM` as separate columns
Statistical aggregate functions (`STDEV`,`STDEVP`,`VAR`, and`VARP`)
`SUM` function that references a nullable expression	Use `ISNULL` inside `SUM()` to make the expression non-nullable
Other aggregate functions (`MIN`,`MAX`,`CHECKSUM_AGG`, and`STRING_AGG`)
User-defined aggregate functions (SQL CLR)

SELECT clause	Transact-SQL element	Possible alternative
`WITH cte AS`	Common table expressions (CTE) `WITH`
`SELECT`	Subqueries
`SELECT`	`SELECT [ <table>. ] *`	Explicitly name columns
`SELECT`	`SELECT DISTINCT`	Use `GROUP BY`
`SELECT`	`SELECT TOP`
`SELECT`	`OVER` clause, which includes ranking or aggregate window functions
`FROM`	`LEFT OUTER JOIN`
`FROM`	`RIGHT OUTER JOIN`
`FROM`	`FULL OUTER JOIN`
`FROM`	`OUTER APPLY`
`FROM`	`CROSS APPLY`
`FROM`	Derived table expressions (that is, using `SELECT` in the `FROM` clause)
`FROM`	Self-joins
`FROM`	Table variables
`FROM`	Inline table-valued function
`FROM`	Multi-statement table-valued function
`FROM`	`PIVOT`, `UNPIVOT`
`FROM`	`TABLESAMPLE`
`FROM`	`FOR SYSTEM_TIME`	Query the temporal history table directly
`WHERE`	Full-text predicates (`CONTAINS`, `FREETEXT`, `CONTAINSTABLE`, `FREETEXTTABLE`)
`GROUP BY`	`CUBE`, `ROLLUP`, or `GROUPING SETS` operators	Define separate indexed views for each combination of `GROUP BY` columns
`GROUP BY`	`HAVING`
Set operators	`UNION`, `UNION ALL`, `EXCEPT`, `INTERSECT`	Use `OR`, `AND NOT`, and `AND` in the `WHERE` clause respectively
`ORDER BY`	`ORDER BY`
`ORDER BY`	`OFFSET`

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.

Important

Indexed views aren't supported on top of temporal queries (queries that use FOR SYSTEM_TIME clause).

Recommendations for datetime and smalldatetime

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. 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 UPDATE, DELETE or INSERT) on a table referenced by a large number of indexed views, or fewer but complex indexed views, those indexed views have to be updated as well during DML execution. As a result, DML query performance can 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 option prevents the optimizer from using the indexes on the views. For more information about the OPTION (EXPAND VIEWS) hint, see SELECT.

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.

Permissions

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 concept is also called an intact ownership chain between the view and the tables. 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, it's 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 AdventureWorks database.

--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 FROM clause.

--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
INNER 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
INNER 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. Before SQL Server 2016 (13.x) Service Pack 1, automatic use of an indexed view by the query optimizer is supported only in specific editions of SQL Server. On SQL Server Standard edition, you must use the NOEXPAND query hint to query the indexed view directly. Since SQL Server 2016 (13.x) Service Pack 1, all editions support automatic use of an indexed view. Azure SQL Database and Azure SQL Managed Instance also support automatic use of indexed views without specifying the NOEXPAND hint. For more information, see Table Hints (Transact-SQL).

--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.

Megosztás a következőn keresztül:

Create indexed views

Steps

Required SET options for indexed views

Deterministic view requirement

Additional requirements

Recommendations for datetime and smalldatetime

Performance considerations with indexed views

Additional considerations

Permissions

Create an indexed view: a T-SQL example

Visszajelzés

További források

Megosztás a következőn keresztül:

Create indexed views

Steps

Required SET options for indexed views

Deterministic view requirement

Additional requirements

Recommendations for datetime and smalldatetime

Performance considerations with indexed views

Additional considerations

Permissions

Create an indexed view: a T-SQL example

Related content

Visszajelzés

További források