CREATE VIEW (Transact-SQL)

Artikel
05/16/2013

Creates a virtual table whose contents (columns and rows) are defined by a query. Use this statement to create a view of the data in one or more tables in the database. For example, a view can be used for the following purposes:

To focus, simplify, and customize the perception each user has of the database.
As a security mechanism by allowing users to access data through the view, without granting the users permissions to directly access the underlying base tables.
To provide a backward compatible interface to emulate a table whose schema has changed.

Topic link icon Transact-SQL Syntax Conventions

Syntax

CREATE VIEW [ schema_name . ] view_name [ (column [ ,...n ] ) ] 
[ WITH <view_attribute> [ ,...n ] ] 
AS select_statement 
[ WITH CHECK OPTION ] [ ; ]

<view_attribute> ::= 
{
    [ ENCRYPTION ]
    [ SCHEMABINDING ]
    [ VIEW_METADATA ]     }

Arguments

schema_name
Is the name of the schema to which the view belongs.
view_name
Is the name of the view. View names must follow the rules for identifiers. Specifying the view owner name is optional.
column
Is the name to be used for a column in a view. A column name is required only when a column is derived from an arithmetic expression, a function, or a constant; when two or more columns may otherwise have the same name, typically because of a join; or when a column in a view is specified a name different from that of the column from which it is derived. Column names can also be assigned in the SELECT statement.

If column is not specified, the view columns acquire the same names as the columns in the SELECT statement.

Note

In the columns for the view, the permissions for a column name apply across a CREATE VIEW or ALTER VIEW statement, regardless of the source of the underlying data. For example, if permissions are granted on the SalesOrderID column in a CREATE VIEW statement, an ALTER VIEW statement can name the SalesOrderID column with a different column name, such as OrderRef, and still have the permissions associated with the view using SalesOrderID.
AS
Specifies the actions the view is to perform.
select_statement
Is the SELECT statement that defines the view. The statement can use more than one table and other views. Appropriate permissions are required to select from the objects referenced in the SELECT clause of the view that is created.

A view does not have to be a simple subset of the rows and columns of one particular table. A view can be created that uses more than one table or other views with a SELECT clause of any complexity.

In an indexed view definition, the SELECT statement must be a single table statement or a multitable JOIN with optional aggregation.

The SELECT clauses in a view definition cannot include the following:
- An ORDER BY clause, unless there is also a TOP clause in the select list of the SELECT statement
  
  Important
  
  The ORDER BY clause is used only to determine the rows that are returned by the TOP or OFFSET clause in the view definition. The ORDER BY clause does not guarantee ordered results when the view is queried, unless ORDER BY is also specified in the query itself.
- The INTO keyword
- The OPTION clause
- A reference to a temporary table or a table variable.
Because select_statement uses the SELECT statement, it is valid to use <join_hint> and <table_hint> hints as specified in the FROM clause. For more information, see FROM (Transact-SQL) and SELECT (Transact-SQL).

Functions and multiple SELECT statements separated by UNION or UNION ALL can be used in select_statement.
CHECK OPTION
Forces all data modification statements executed against the view to follow the criteria set within select_statement. When a row is modified through a view, the WITH CHECK OPTION makes sure the data remains visible through the view after the modification is committed.

Note

Any updates performed directly to a view's underlying tables are not verified against the view, even if CHECK OPTION is specified.
ENCRYPTION
Encrypts the entries in sys.syscomments that contain the text of the CREATE VIEW statement. Using WITH ENCRYPTION prevents the view from being published as part of SQL Server replication.
SCHEMABINDING
Binds the view to the schema of the underlying table or tables. When SCHEMABINDING is specified, the base table or tables cannot be modified in a way that would affect the view definition. The view definition itself must first be modified or dropped to remove dependencies on the table that is to be modified. When you use SCHEMABINDING, the select_statement must include the two-part names (schema**.**object) of tables, views, or user-defined functions that are referenced. All referenced objects must be in the same database.

Views or tables that participate in a view created with the SCHEMABINDING clause cannot be dropped unless that view is dropped or changed so that it no longer has schema binding. Otherwise, the Database Engine raises an error. Also, executing ALTER TABLE statements on tables that participate in views that have schema binding fail when these statements affect the view definition.
VIEW_METADATA
Specifies that the instance of SQL Server will return to the DB-Library, ODBC, and OLE DB APIs the metadata information about the view, instead of the base table or tables, when browse-mode metadata is being requested for a query that references the view. Browse-mode metadata is additional metadata that the instance of SQL Server returns to these client-side APIs. This metadata enables the client-side APIs to implement updatable client-side cursors. Browse-mode metadata includes information about the base table that the columns in the result set belong to.

For views created with VIEW_METADATA, the browse-mode metadata returns the view name and not the base table names when it describes columns from the view in the result set.

When a view is created by using WITH VIEW_METADATA, all its columns, except a timestamp column, are updatable if the view has INSTEAD OF INSERT or INSTEAD OF UPDATE triggers. For more information about updatable views, see Remarks.

Remarks

A view can be created only in the current database. The CREATE VIEW must be the first statement in a query batch. A view can have a maximum of 1,024 columns.

When querying through a view, the Database Engine checks to make sure that all the database objects referenced anywhere in the statement exist and that they are valid in the context of the statement, and that data modification statements do not violate any data integrity rules. A check that fails returns an error message. A successful check translates the action into an action against the underlying table or tables.

If a view depends on a table or view that was dropped, the Database Engine produces an error message when anyone tries to use the view. If a new table or view is created and the table structure does not change from the previous base table to replace the one dropped, the view again becomes usable. If the new table or view structure changes, the view must be dropped and re-created.

If a view is not created with the SCHEMABINDING clause, sp_refreshview should be run when changes are made to the objects underlying the view that affect the definition of the view. Otherwise, the view might produce unexpected results when it is queried.

When a view is created, information about the view is stored in the following catalog views: sys.views, sys.columns, and sys.sql_expression_dependencies. The text of the CREATE VIEW statement is stored in the sys.sql_modules catalog view.

A query that uses an index on a view defined with numeric or float expressions may have a result that is different from a similar query that does not use the index on the view. This difference may be caused by rounding errors during INSERT, DELETE, or UPDATE actions on underlying tables.

The Database Engine saves the settings of SET QUOTED_IDENTIFIER and SET ANSI_NULLS when a view is created. These original settings are used to parse the view when the view is used. Therefore, any client-session settings for SET QUOTED_IDENTIFIER and SET ANSI_NULLS do not affect the view definition when the view is accessed.

Updatable Views

You can modify the data of an underlying base table through a view, as long as the following conditions are true:

Any modifications, including UPDATE, INSERT, and DELETE statements, must reference columns from only one base table.
The columns being modified in the view must directly reference the underlying data in the table columns. The columns cannot be derived in any other way, such as through the following:
- An aggregate function: AVG, COUNT, SUM, MIN, MAX, GROUPING, STDEV, STDEVP, VAR, and VARP.
- A computation. The column cannot be computed from an expression that uses other columns. Columns that are formed by using the set operators UNION, UNION ALL, CROSSJOIN, EXCEPT, and INTERSECT amount to a computation and are also not updatable.
The columns being modified are not affected by GROUP BY, HAVING, or DISTINCT clauses.
TOP is not used anywhere in the select_statement of the view together with the WITH CHECK OPTION clause.

The previous restrictions apply to any subqueries in the FROM clause of the view, just as they apply to the view itself. Generally, the Database Engine must be able to unambiguously trace modifications from the view definition to one base table. For more information, see Modify Data Through a View.

If the previous restrictions prevent you from modifying data directly through a view, consider the following options:

INSTEAD OF Triggers

INSTEAD OF triggers can be created on a view to make a view updatable. The INSTEAD OF trigger is executed instead of the data modification statement on which the trigger is defined. This trigger lets the user specify the set of actions that must happen to process the data modification statement. Therefore, if an INSTEAD OF trigger exists for a view on a specific data modification statement (INSERT, UPDATE, or DELETE), the corresponding view is updatable through that statement. For more information about INSTEAD OF triggers, see DML Triggers.
Partitioned Views

If the view is a partitioned view, the view is updatable, subject to certain restrictions. When it is needed, the Database Engine distinguishes local partitioned views as the views in which all participating tables and the view are on the same instance of SQL Server, and distributed partitioned views as the views in which at least one of the tables in the view resides on a different or remote server.

Partitioned Views

A partitioned view is a view defined by a UNION ALL of member tables structured in the same way, but stored separately as multiple tables in either the same instance of SQL Server or in a group of autonomous instances of SQL Server servers, called federated database servers.

Note

The preferred method for partitioning data local to one server is through partitioned tables. For more information, see Partitioned Tables and Indexes.

In designing a partitioning scheme, it must be clear what data belongs to each partition. For example, the data for the Customers table is distributed in three member tables in three server locations: Customers_33 on Server1, Customers_66 on Server2, and Customers_99 on Server3.

A partitioned view on Server1 is defined in the following way:

--Partitioned view as defined on Server1
CREATE VIEW Customers
AS
--Select from local member table.
SELECT *
FROM CompanyData.dbo.Customers_33
UNION ALL
--Select from member table on Server2.
SELECT *
FROM Server2.CompanyData.dbo.Customers_66
UNION ALL
--Select from mmeber table on Server3.
SELECT *
FROM Server3.CompanyData.dbo.Customers_99;

Generally, a view is said to be a partitioned view if it is of the following form:

SELECT <select_list1>
FROM T1
UNION ALL
SELECT <select_list2>
FROM T2
UNION ALL
...
SELECT <select_listn>
FROM Tn;

Conditions for Creating Partitioned Views

The select list
- All columns in the member tables should be selected in the column list of the view definition.
- The columns in the same ordinal position of each select list should be of the same type, including collations. It is not sufficient for the columns to be implicitly convertible types, as is generally the case for UNION.
  
  Also, at least one column (for example <col>) must appear in all the select lists in the same ordinal position. This <col> should be defined in a way that the member tables T1, ..., Tn have CHECK constraints C1, ..., Cn defined on <col>, respectively.
  
  Constraint C1 defined on table T1 must be of the following form:
```
C1 ::= < simple_interval > [ OR < simple_interval > OR ...]
< simple_interval > :: = 
< col > { < | > | <= | >= | = < value >} 
| < col > BETWEEN < value1 > AND < value2 >
| < col > IN ( value_list )
| < col > { > | >= } < value1 > AND
< col > { < | <= } < value2 >
```
- The constraints should be in such a way that any specified value of <col> can satisfy, at most, one of the constraints C1, ..., Cn so that the constraints should form a set of disjointed or nonoverlapping intervals. The column <col> on which the disjointed constraints are defined is called the partitioning column. Note that the partitioning column may have different names in the underlying tables. The constraints should be in an enabled and trusted state for them to meet the previously mentioned conditions of the partitioning column. If the constraints are disabled, re-enable constraint checking by using the CHECK CONSTRAINT constraint_name option of ALTER TABLE, and using the WITH CHECK option to validate them.
  
  The following examples show valid sets of constraints:
```
{ [col < 10], [col between 11 and 20] , [col > 20] }
{ [col between 11 and 20], [col between 21 and 30], [col between 31 and 100] }
```
- The same column cannot be used multiple times in the select list.
Partitioning column
- The partitioning column is a part of the PRIMARY KEY of the table.
- It cannot be a computed, identity, default, or timestamp column.
- If there is more than one constraint on the same column in a member table, the Database Engine ignores all the constraints and does not consider them when determining whether the view is a partitioned view. To meet the conditions of the partitioned view, there should be only one partitioning constraint on the partitioning column.
- There are no restrictions on the updatability of the partitioning column.
Member tables, or underlying tables T1, ..., Tn
- The tables can be either local tables or tables from other computers that are running SQL Server that are referenced either through a four-part name or an OPENDATASOURCE- or OPENROWSET-based name. The OPENDATASOURCE and OPENROWSET syntax can specify a table name, but not a pass-through query. For more information, see OPENDATASOURCE (Transact-SQL) and OPENROWSET (Transact-SQL).
  
  If one or more of the member tables are remote, the view is called distributed partitioned view, and additional conditions apply. They are described later in this section.
- The same table cannot appear two times in the set of tables that are being combined with the UNION ALL statement.
- The member tables cannot have indexes created on computed columns in the table.
- The member tables should have all PRIMARY KEY constraints on the same number of columns.
- All member tables in the view should have the same ANSI padding setting. This can be set by using either the user options option in sp_configure or the SET statement.

Conditions for Modifying Data in Partitioned Views

The following restrictions apply to statements that modify data in partitioned views:

The INSERT statement must supply values for all the columns in the view, even if the underlying member tables have a DEFAULT constraint for those columns or if they allow for null values. For those member table columns that have DEFAULT definitions, the statements cannot explicitly use the keyword DEFAULT.
The value being inserted into the partitioning column should satisfy at least one of the underlying constraints; otherwise, the insert action will fail with a constraint violation.
UPDATE statements cannot specify the DEFAULT keyword as a value in the SET clause, even if the column has a DEFAULT value defined in the corresponding member table.
Columns in the view that are an identity column in one or more of the member tables cannot be modified by using an INSERT or UPDATE statement.
If one of the member tables contains a timestamp column, the data cannot be modified by using an INSERT or UPDATE statement.
If one of the member tables contains a trigger or an ON UPDATE CASCADE/SET NULL/SET DEFAULT or ON DELETE CASCADE/SET NULL/SET DEFAULT constraint, the view cannot be modified.
INSERT, UPDATE, and DELETE actions against a partitioned view are not allowed if there is a self-join with the same view or with any of the member tables in the statement.
Bulk importing data into a partitioned view is unsupported by bcp or the BULK INSERT and INSERT ... SELECT * FROM OPENROWSET(BULK...) statements. However, you can insert multiple rows into a partitioned view by using the INSERT statement.

Note

To update a partitioned view, the user must have INSERT, UPDATE, and DELETE permissions on the member tables.

Additional Conditions for Distributed Partitioned Views

For distributed partitioned views (when one or more member tables are remote), the following additional conditions apply:

A distributed transaction will be started to guarantee atomicity across all nodes affected by the update.
The XACT_ABORT SET option should be set to ON for INSERT, UPDATE, or DELETE statements to work.
Any columns in remote tables of type smallmoney that are referenced in a partitioned view are mapped as money. Therefore, the corresponding columns (in the same ordinal position in the select list) in the local tables must also be of type money.
Under database compatibility level 110, any columns in remote tables of type smalldatetime that are referenced in a partitioned view are mapped as smalldatetime. Corresponding columns (in the same ordinal position in the select list) in the local tables must be smalldatetime. This is a change in behavior from earlier versions of SQL Server in which any columns in remote tables of type smalldatetime that are referenced in a partitioned view are mapped as datetime and corresponding columns in local tables must be of type datetime. For more information, see ALTER DATABASE Compatibility Level (Transact-SQL).
Any linked server in the partitioned view cannot be a loopback linked server. This is a linked server that points to the same instance of SQL Server.

The setting of the SET ROWCOUNT option is ignored for INSERT, UPDATE, and DELETE actions that involve updatable partitioned views and remote tables.

When the member tables and partitioned view definition are in place, the SQL Server query optimizer builds intelligent plans that use queries efficiently to access data from member tables. With the CHECK constraint definitions, the query processor maps the distribution of key values across the member tables. When a user issues a query, the query processor compares the map to the values specified in the WHERE clause, and builds an execution plan with a minimal amount of data transfer between member servers. Therefore, although some member tables may be located in remote servers, the instance of SQL Server resolves distributed queries so that the amount of distributed data that has to be transferred is minimal.

Considerations for Replication

To create partitioned views on member tables that are involved in replication, the following considerations apply:

If the underlying tables are involved in merge replication or transactional replication with updating subscriptions, the uniqueidentifier column should also be included in the select list.

Any INSERT actions into the partitioned view must provide a NEWID() value for the uniqueidentifier column. Any UPDATE actions against the uniqueidentifier column must supply NEWID() as the value because the DEFAULT keyword cannot be used.
The replication of updates made by using the view is the same as when tables are replicated in two different databases: the tables are served by different replication agents and the order of the updates is not guaranteed.

Permissions

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

Examples

A. Using a simple CREATE VIEW

The following example creates a view by using a simple SELECT statement. A simple view is helpful when a combination of columns is queried frequently. The data from this view comes from the HumanResources.Employee and Person.Person tables of the AdventureWorks2012 database. The data provides name and hire date information for the employees of Adventure Works Cycles. The view could be created for the person in charge of tracking work anniversaries but without giving this person access to all the data in these tables.

USE AdventureWorks2012 ;
GO
IF OBJECT_ID ('hiredate_view', 'V') IS NOT NULL
DROP VIEW hiredate_view ;
GO
CREATE VIEW hiredate_view
AS 
SELECT p.FirstName, p.LastName, e.BusinessEntityID, e.HireDate
FROM HumanResources.Employee e 
JOIN Person.Person AS p ON e.BusinessEntityID = p.BusinessEntityID ;
GO

B. Using WITH ENCRYPTION

The following example uses the WITH ENCRYPTION option and shows computed columns, renamed columns, and multiple columns.

USE AdventureWorks2012 ;
GO
IF OBJECT_ID ('Purchasing.PurchaseOrderReject', 'V') IS NOT NULL
    DROP VIEW Purchasing.PurchaseOrderReject ;
GO
CREATE VIEW Purchasing.PurchaseOrderReject
WITH ENCRYPTION
AS
SELECT PurchaseOrderID, ReceivedQty, RejectedQty, 
    RejectedQty / ReceivedQty AS RejectRatio, DueDate
FROM Purchasing.PurchaseOrderDetail
WHERE RejectedQty / ReceivedQty > 0
AND DueDate > CONVERT(DATETIME,'20010630',101) ;
GO

C. Using WITH CHECK OPTION

The following example shows a view named SeattleOnly that references five tables and allows for data modifications to apply only to employees who live in Seattle.

USE AdventureWorks2012 ;
GO
IF OBJECT_ID ('dbo.SeattleOnly', 'V') IS NOT NULL
    DROP VIEW dbo.SeattleOnly ;
GO
CREATE VIEW dbo.SeattleOnly
AS
SELECT p.LastName, p.FirstName, e.JobTitle, a.City, sp.StateProvinceCode
FROM HumanResources.Employee e
    INNER JOIN Person.Person p
    ON p.BusinessEntityID = e.BusinessEntityID
    INNER JOIN Person.BusinessEntityAddress bea 
    ON bea.BusinessEntityID = e.BusinessEntityID 
    INNER JOIN Person.Address a 
    ON a.AddressID = bea.AddressID
    INNER JOIN Person.StateProvince sp 
    ON sp.StateProvinceID = a.StateProvinceID
WHERE a.City = 'Seattle'
WITH CHECK OPTION ;
GO

D. Using built-in functions within a view

The following example shows a view definition that includes a built-in function. When you use functions, you must specify a column name for the derived column.

USE AdventureWorks2012 ;
GO
IF OBJECT_ID ('Sales.SalesPersonPerform', 'V') IS NOT NULL
    DROP VIEW Sales.SalesPersonPerform ;
GO
CREATE VIEW Sales.SalesPersonPerform
AS
SELECT TOP (100) SalesPersonID, SUM(TotalDue) AS TotalSales
FROM Sales.SalesOrderHeader
WHERE OrderDate > CONVERT(DATETIME,'20001231',101)
GROUP BY SalesPersonID;
GO

E. Using partitioned data

The following example uses tables named SUPPLY1, SUPPLY2, SUPPLY3, and SUPPLY4. These tables correspond to the supplier tables from four offices, located in different countries/regions.

--Create the tables and insert the values.
CREATE TABLE dbo.SUPPLY1 (
supplyID INT PRIMARY KEY CHECK (supplyID BETWEEN 1 and 150),
supplier CHAR(50)
);
CREATE TABLE dbo.SUPPLY2 (
supplyID INT PRIMARY KEY CHECK (supplyID BETWEEN 151 and 300),
supplier CHAR(50)
);
CREATE TABLE dbo.SUPPLY3 (
supplyID INT PRIMARY KEY CHECK (supplyID BETWEEN 301 and 450),
supplier CHAR(50)
);
CREATE TABLE dbo.SUPPLY4 (
supplyID INT PRIMARY KEY CHECK (supplyID BETWEEN 451 and 600),
supplier CHAR(50)
);
GO
INSERT dbo.SUPPLY1 VALUES ('1', 'CaliforniaCorp'), ('5', 'BraziliaLtd');
INSERT dbo.SUPPLY2 VALUES ('231', 'FarEast'), ('280', 'NZ');
INSERT dbo.SUPPLY3 VALUES ('321', 'EuroGroup'), ('442', 'UKArchip');
INSERT dbo.SUPPLY4 VALUES ('475', 'India'), ('521', 'Afrique');
GO
--Create the view that combines all supplier tables.
CREATE VIEW dbo.all_supplier_view
WITH SCHEMABINDING
AS
SELECT supplyID, supplier
FROM dbo.SUPPLY1
UNION ALL
SELECT supplyID, supplier
FROM dbo.SUPPLY2
UNION ALL
SELECT supplyID, supplier
FROM dbo.SUPPLY3
UNION ALL
SELECT supplyID, supplier
FROM dbo.SUPPLY4;

Dela via