Microsoft SQL Server 2008 R2 Unleashed- P91 docx

Creating Views Using T-SQL The CREATE VIEW statement is used to create views with T-SQL.. The following example shows the creation of one of the prior views with the ENCRYPTION attribute

adventure-works\rachel0 1965-08-09 F 2003-07-01 1

Only the rows in the Employee table with a HireDate value greater than March 1, 2003,

are returned when you select everything from the view Separate views can be created

based on geography, demographics, or any other data element that requires a different set

of security

Keep in mind that additional conditions can be applied when selecting from a view You

can utilize another WHERE clause in the SELECT statement that uses a view This is

demon-strated in the following example:

select * from EmpViewHorizontal

where HireDate >= ‘7/1/03’

and BirthDate > ‘1/1/65’

LoginID BirthDate Gender HireDate SalariedFlag

adventure-works\rachel0 1965-08-09 F 2003-07-01 1

As you can see, a view with horizontal security restricts your initial result set but does not

prevent you from applying additional conditions to obtain the desired result

Creating Views

You can create several different types of views in SQL Server 2008, including standard

views, indexed views, and partitioned views Standard views are like those that have been

discussed thus far in this chapter; they let you achieve most of the benefits associated with

views An indexed view has a unique clustered index defined on it that causes the view to

be materialized In other words, the creation of the index causes physical storage of the

data related to the view’s index Partitioned views join horizontally partitioned data from

a set of distinct tables They can be locally partitioned, meaning that the tables are on the

same server; or they can be distributed, meaning that some of the tables exist on other

servers Partitioned views and indexed views are discussed in detail later in this chapter

All types of views share a common set of restrictions:

Every column (including derived columns) must have a name

The SELECT statement used in the view cannot include the COMPUTE BY clause or the

INTO keyword

The SELECT statement used in the view cannot include the ORDER BY clause

The SELECT statement used in the view cannot contain temporary tables

You cannot associate AFTER triggers with views, but you can associate INSTEAD OF

triggers

A view can have a maximum of 1,024 columns You can select all the columns for a view

by using a SELECT * statement, but you need to use some caution when doing so In

particular, you must keep in mind that the view will not display columns that have been

added to the view’s underlying tables after the view has been created The fact that the

new columns are not displayed can be a good thing but is sometimes overlooked You can

prevent changes to the underlying objects (for example, tables) by creating the view with

SCHEMABINDING SCHEMABINDING is discussed in the next section

If you want the changes to the underlying objects to be reflected in the views, you can use

the sp_refreshview stored procedure This stored procedure updates the metadata for the

specified non-schema-bound view

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SQL Server Books Online lists a handy script that can be used to update any view that

has a dependency on an object The script is shown in the sp_refreshview examples

The script, listed here, is coded such that it will generate output that can be run to

generate the sp_refreshview statements for the Person.Person table in the

Adventureworks2008 database:

SELECT DISTINCT ‘EXEC sp_refreshview ‘’’ + name + ‘’’’

FROM sys.objects so INNER JOIN sys.sql_dependencies sd

ON so.object_id = sd.object_id

WHERE type = ‘V’

AND sd.referenced_major_id = object_id(‘Person.Person’)

To generate the executions for another object, you simply change the name of the

object (that is, Person.Person) found at the end of the script to the name of the

object you want to investigate

With these guidelines in mind, you are now ready to create your view Views can be

created in SQL Server 2008 using T-SQL or SQL Server Management Studio (SSMS)

Creating Views Using T-SQL

The CREATE VIEW statement is used to create views with T-SQL The syntax for the CREATE

VIEW statement follows:

CREATE VIEW [ schema_name ] view_name [ (column [ , n ] ) ]

[ WITH <view_attribute> [ , n ] ]

AS select_statement [ ; ]

[ WITH CHECK OPTION ]

<view_attribute> ::=

{

[ ENCRYPTION ]

[ SCHEMABINDING ]

[ VIEW_METADATA ] }

This statement and the related options are essentially the same in SQL Server 2008 as they

were in SQL Server 2005 and SQL Server 2000 We first look at a simple example for

creat-ing a view with T-SQL and then delve into several other examples that utilize the view

attributes Listing 27.2 shows a sample T-SQL statement for creating a simple view

CREATE VIEW Sales.vw_OrderSummary as

select datepart(yy, orderdate) as ‘OrderYear’,

datepart(mm, orderdate) as ‘OrderMonth’,

sum(TotalDue) as ‘OrderTotal’

from Sales.SalesOrderHeader

group by datepart(yy, orderdate), datepart(mm, orderdate)

There are several important aspects to notice in the example in Listing 27.2 First, all the

columns in the SELECT statement are derived columns and do not simply reference a

column in a table You do not need to have a derived column in your view, but if you do,

the derived column(s) must have a name or an alias assigned to it to be able to create the

view The column name allows you to reference the derived column when selecting from

the view If the derived columns in the SELECT statement are not named, the CREATE VIEW

statement will fail

Another notable characteristic of the simple view example is that an aggregate is used in

the SELECT statement Aggregates are allowed in views and are common implementations

of views Views with aggregates can be used instead of summary tables that denormalize

data and use additional disk space Keep in mind that the results of any view (including

those with aggregates) are not returned in any particular order Views cannot be created

with the ORDER BY clause, but the ORDER BY clause can be utilized in a SELECT statement

that references the view The following example shows the first five rows of the

vw_OrderSummary view created in Listing 27.2:

select top 5 * from Sales.vw_OrderSummary

OrderYear OrderMonth OrderTotal

—————- —————-

——————————-2003 5 4449886.2315

2001 11 3690018.6652

2003 8 6775857.0745

2002 7 3781879.0708

2003 11 5961182.6761

You can see from the results of the SELECT that the summarized order information is not

returned in any particular order If you want to sort the results, you can treat the view like

a table in a SELECT statement and use the ORDER BY clause to produce the desired results

The following example shows a SELECT statement from the vw_OrderSummary view and the

ordered results:

select top 5 *

from Sales.vw_OrderSummary

where OrderYear >= 2004

order by OrderYear, OrderMonth

OrderYear OrderMonth OrderTotal

—————- —————-

——————————-2004 1 3691013.2227

2004 2 5207182.5122

2004 3 5272786.8106

2004 4 4722890.7352

2004 5 6518825.2262

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In many cases, it is best to create views that include the primary key columns from the

underlying tables This allows the views to be joined to other tables Consider, for

example, a view created on the Employee table in the Adventureworks2008 database

If you want to join that view to another table (such as EmployeeAddress), you need the

primary key of the table (that is, Employee.EmployeeID) in the view

Views can also be created with the following special view attributes: ENCRYPTION,

SCHEMABINDING, and VIEW_METADATA Each of these attributes and some other specialized

views are discussed in the following sections

ENCRYPTION

The ENCRYPTION attribute causes the view definition to be stored as encrypted text in

sys.syscomments This feature is also available for stored procedures and other database

code that you may want to protect One issue to consider when you create a view using

the ENCRYPTION option is that this option prevents the view from being published as part

of SQL Server replication

The following example shows the creation of one of the prior views with the

ENCRYPTION attribute:

IF EXISTS (SELECT * FROM sys.views WHERE

object_id = OBJECT_ID(N’[Sales].[vw_OrderSummary]’))

DROP VIEW [Sales].[vw_OrderSummary]

GO

CREATE VIEW Sales.vw_OrderSummary

WITH ENCRYPTION AS

select datepart(yy, orderdate) as ‘OrderYear’,

datepart(mm, orderdate) as ‘OrderMonth’,

sum(TotalDue) as ‘OrderTotal’

from Sales.SalesOrderHeader

group by datepart(yy, orderdate), datepart(mm, orderdate)

go

The following SELECT statement from sys.syscomments retrieves the text related to the

encrypted view and shows that the view definition is not visible in the Text column:

SELECT id, OBJECT_NAME(ID) ‘ViewName’, text

FROM SYS.sysCOMMENTS

WHERE OBJECT_NAME(ID) LIKE ‘%vw_OrderSummary%’

id ViewName text

—————— ——————————— ———————————

919674324 vw_OrderSummary NULL

SCHEMABINDING

The SCHEMABINDING attribute binds a view to the schema of the underlying table(s)

refer-enced in the view’s SELECT statement This binding action prevents any changes to the

underlying tables that would affect the view definition For example, if you have a view

that includes the Employee.Title column, this column cannot be altered or dropped in

the Employee table If schema changes are attempted on the underlying tables, an error

message is returned, and the change is not allowed The only way to make the change is

to drop the view or alter the view to remove the SCHEMABINDING attribute

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Views created with SCHEMABINDING have been used in the past to simply prevent

changes to the underlying schema Any table for which you wanted to prevent schema

changes was included in a view, and this essentially locked the definition of the table

This approach is no longer needed because you can accomplish the same thing using

VIEW_METADATA

When the VIEW_METADATA option is specified, SQL Server returns information about the

view, as opposed to the base tables This happens when browse-mode metadata is

requested for a query that references the view via a database API Browse-mode metadata

is additional information returned by SQL Server to client-side DBLIB, ODBC, and OLE DB

APIs, which allows them to implement client-side updatable cursors

WITH CHECK OPTION

WITH CHECK OPTION forces all data modifications made through a view to adhere to the

conditions in the view The example shown in Listing 27.3 shows a view created using

WITH CHECK OPTION

CREATE VIEW HumanResources.vw_MaleEmployees

AS

SELECT LoginID, Gender

FROM HumanResources.Employee

WHERE Gender = 'M'

WITH CHECK OPTION

The following UPDATE statement fails when executed against the view created in Listing

27.3 because the Gender change would cause it to no longer be seen by the view:

UPDATE HumanResources.vw_MaleEmployees

SET Gender = ‘F’

WHERE LoginId = ‘adventure-works\taylor0’

Updates and other modifications made though a view are discussed further in the “Data

Modifications and Views” section, later in this chapter

Creating Views Using the View Designer

SQL Server 2008 provides a graphical tool, called the View Designer, you can use to create

views This tool can be an invaluable aid when you are creating or modifying a view The

View Designer is equipped with four panes that provide the information relative to the

view Figure 27.1 shows the View Designer display for the Person

vStateProvinceCountryRegion view installed in the Adventureworks2008 database To

view an existing view in the View Designer, right-click on the view listed in the Object

Explorer and select Design To create a new view via the View Designer, right-click the

Views node in the Object Explorer and select New View An empty View Designer is

displayed

The View Designer has these four panes:

Diagram pane—Gives a graphical view of the tables that are part of the view This

includes the columns in the tables and relationships between the tables contained

in the view

Criteria pane—Displays all the columns selected in the view and allows for sorting,

filtering, and other related column-oriented criteria

SQL pane—Renders the T-SQL associated with the view.

Results pane—Shows the results of that view’s SELECT statement

The panes in the View Designer are dependent on each other If you add a WHERE clause in

the SQL pane, the corresponding Filter value is added in the Criteria pane Similarly, if

you right-click in the Diagram pane and add a table to the view, the Criteria and SQL

panes are updated to reflect this change

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One of the most amazing features of the View Designer is the capability to render a

SQL statement into its graphical form You can copy T-SQL into the SQL pane, and the

View Designer reverse-engineers the tables into the Diagram pane, giving you a

You can control the View Designer via the Query Designer menu option as well Adding a

new table, verifying the T-SQL, and changing the panes displayed are just some of the

options available on this menu

NOTE

The View Designer does not allow you to set every attribute of a view It is a great

starting point for creating a view, but you need to set some attributes using T-SQL after

creating the view For example, you cannot specify WITH CHECK OPTION in the View

Designer, but you can set it by altering the view after it has been created

There is also no option to script a view from the View Designer You must close the

View Designer first, and then you are asked whether you want to save the view If you

click Yes, a prompt allows you to specify a name

The Properties window displays information about the view and also allows you to enter

additional view properties If this window is not visible, you can select the Properties

window from the View menu or simply press F4 The properties you can set on the view

include (but are not limited to) a description, the schema that owns the view, and

whether to bind the view to the schema Figure 27.2 shows the Properties window for the

Person.vStateProvinceCountryRegion view that we looked at earlier

After defining a view using the panes in the View Designer and setting its properties, you

can choose to save the view You are prompted to give it a name After you save the view,

Managing Views

After creating your view, you can manage the view via SQL or the View Designer The

T-SQL commands for managing views are the ALTER VIEW and DROP VIEW statements The

ALTER VIEW statement is used to modify the properties or definition of the view, and the

DROP VIEW statement is used to remove the view from the database

Altering Views with T-SQL

The ALTER VIEW syntax follows:

ALTER VIEW [ schema_name ] view_name [ ( column [ , n ] ) ]

[ WITH <view_attribute> [ , n ] ]

AS select_statement [ ; ]

[ WITH CHECK OPTION ]

<view_attribute> ::=

{

[ ENCRYPTION ]

[ SCHEMABINDING ]

[ VIEW_METADATA ]

}

The ALTER VIEW statement utilizes the same set of options and parameters as the CREATE

VIEW statement You should consider using the ALTER VIEW statement when making

changes to your view instead of dropping and re-creating the view Altered views retain

their associated permissions and do not affect dependent stored procedures or triggers

An example of the ALTER VIEW statement follows:

ALTER VIEW [dbo].[vw_employee]

with SCHEMABINDING

AS

SELECT TITLE, GENDER

FROM HumanResources.Employee

WITH CHECK OPTION

The entire definition of the view, including any attributes or options, must be listed in the

ALTER VIEW statement This behavior is similar to that of the ALTER PROCEDURE statement

and some of the other ALTER statements You can generate the ALTER VIEW statement from

the Object Explorer by right-clicking the view and selecting Script View As and then

choosing Alter To This allows you to script the ALTER statement to a new query editor

window, a file, or the Clipboard

Dropping Views with T-SQL

You can drop views from a database by using the DROP VIEW statement The syntax for

DROP VIEW follows:

DROP VIEW [ schema_name ] view_name [ ,n ] [ ; ]

You can drop more than one view by using one DROP VIEW statement and listing all the

targeted views, separated by commas You should consider running the sp_depends stored

procedure against the targeted views before dropping them This procedure lists the

objects dependent on the view you are dropping

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You can also drop more than one view via SSMS Simply select the Views node in

Object Explorer and then activate the Object Explorer Details window The Object

Explorer Details window displays all the views and allows you to select multiple views

that are displayed After selecting the views you want to delete, you can right-click a

selection and choose Delete to remove all the views selected

Managing Views with SSMS

You can use the Object Explorer in SQL Server Management Studio to alter or drop views

as well To do so, you right-click a view in the Object Explorer and choose Design to

launch the View Designer The View Designer allows you to modify a view in an

easy-to-use graphical interface Refer to the “Creating Views Using the View Designer” section,

earlier in this chapter, for a detailed review of the View Designer

To drop a view, you right-click the view in the Object Explorer and choose Delete You can

drop the view by clicking OK on the Delete Object screen, or you can script the drop

state-ment for later execution

Data Modifications and Views

Data modifications are allowed through a view under certain circumstances Views that

meet these criteria are sometimes called updatable views Updatable views can be

refer-enced in an INSERT, UPDATE, or DELETE statement, and these statements ultimately affect

the underlying table(s) in the view

The following example contains a SQL statement to create an updatable view, followed by

an UPDATE statement that performs a data modification using the view:

CREATE VIEW vw_CreditCard

AS

SELECT CreditCardID, CardType, CardNumber, ExpMonth, ExpYear