module 8: implementing views. overview introduction advantages definition modifying data through...

Module 8: Implementing Views

Overview

Introduction

Advantages

Definition

Modifying Data Through Views

Optimizing Performance by Using Views

Introduction to Views

EmployeeViewEmployeeViewEmployeeViewEmployeeView

Lastname Lastname Firstname Firstname

Davolio Fuller Leverling

Davolio Fuller Leverling

Nancy Andrew Janet

Nancy Andrew Janet

EmployeesEmployeesEmployeesEmployees

EmployeeIDEmployeeID LastName LastName FirstnameFirstname TitleTitle

123

123

DavolioFullerLeverling

DavolioFullerLeverling

NancyAndrewJanet

NancyAndrewJanet

~~~~~~~~~

~~~~~~~~~

User’s ViewUser’s View

USE NorthwindGOCREATE VIEW dbo.EmployeeViewAS SELECT LastName, FirstnameFROM Employees

USE NorthwindGOCREATE VIEW dbo.EmployeeViewAS SELECT LastName, FirstnameFROM Employees

Advantages of Views

Focus the Data for Users Focus on important or appropriate data only Limit access to sensitive data (hide SSN from professors)

Mask Database Complexity Hide complex database design Simplify complex queries, including distributed queries to

heterogeneous data by embedding them in views Simplify Management of User Permissions

Different user access DB from different views Improve Performance

Reduce data access Organize Data for Export to Other Applications

Defining Views

Creating Views

Example: View of Joined Tables

Altering and Dropping Views

Avoiding Broken Ownership Chains

Locating View Definition Information

Hiding View Definitions

Creating Views

Creating a View

Restrictions on View Definitions

Cannot include ORDER BY clause Cannot include INTO keyword

CREATE VIEW dbo.OrderSubtotalsView (OrderID, Subtotal)ASSELECT OD.OrderID, SUM(CONVERT(money,(OD.UnitPrice*Quantity*(1-Discount)/100))*100)FROM [Order Details] ODGROUP BY OD.OrderIDGO

CREATE VIEW dbo.OrderSubtotalsView (OrderID, Subtotal)ASSELECT OD.OrderID, SUM(CONVERT(money,(OD.UnitPrice*Quantity*(1-Discount)/100))*100)FROM [Order Details] ODGROUP BY OD.OrderIDGO

Example: View of Joined Tables

OrderIDOrderIDOrderIDOrderID

1066310827104271045110515

1066310827104271045110515

CustomerIDCustomerIDCustomerIDCustomerID

BONAP BONAP PICCO QUICKQUICK

BONAP BONAP PICCO QUICKQUICK

~~~ ~~~ ~~~ ~~~ ~~~

~~~ ~~~ ~~~ ~~~ ~~~

RequiredDateRequiredDateRequiredDateRequiredDate

1997-09-241998-01-261997-02-241997-03-051997-05-07

1997-09-241998-01-261997-02-241997-03-051997-05-07

ShippedDateShippedDateShippedDateShippedDate

1997-10-031998-02-061997-03-031997-03-121997-05-23

1997-10-031998-02-061997-03-031997-03-121997-05-23

Orders Customers

ShipStatusViewUSE NorthwindGOCREATE VIEW dbo.ShipStatusViewASSELECT OrderID, ShippedDate, ContactNameFROM Customers C INNER JOIN Orders O ON C.CustomerID = O.CustomerIDWHERE RequiredDate < ShippedDate

USE NorthwindGOCREATE VIEW dbo.ShipStatusViewASSELECT OrderID, ShippedDate, ContactNameFROM Customers C INNER JOIN Orders O ON C.CustomerID = O.CustomerIDWHERE RequiredDate < ShippedDate

CustomerIDCustomerIDCustomerIDCustomerID

BONAPPICCOQUICK

BONAPPICCOQUICK

CompanyNameCompanyNameCompanyNameCompanyName

Bon app'Piccolo und mehrQUICK-Stop

Bon app'Piccolo und mehrQUICK-Stop

ContactNameContactNameContactNameContactName

Laurence LebihanGeorg PippsHorst Kloss


OrderIDOrderIDOrderIDOrderID

102641027110280

102641027110280

1996-08-211996-08-291996-09-11

1996-08-211996-08-291996-09-11

ShippedDateShippedDateShippedDateShippedDate

1996-08-231996-08-301996-09-12

1996-08-231996-08-301996-09-12

ContactNameContactNameContactNameContactName



Altering and Dropping Views

Altering Views

Retains assigned permissions

Causes new SELECT statement and options to replace existing definition

Dropping Views

USE NorthwindGOALTER VIEW dbo.EmployeeViewAS SELECT LastName, FirstName, ExtensionFROM Employees

USE NorthwindGOALTER VIEW dbo.EmployeeViewAS SELECT LastName, FirstName, ExtensionFROM Employees

DROP VIEW dbo.ShipStatusViewDROP VIEW dbo.ShipStatusView

GRANT SELECT ON view2 TO azharGRANT SELECT ON view2 TO azhar

SELECT * FROM reif.view2SELECT * FROM reif.view2

Dependent Objects with Different Owners

Example:

Reif executes:

Azhar executes:

Avoiding Broken Ownership Chains

reif.view2

lewis.view1

lewis.table1

azhar does not have rights tolewis.view1 and lewis.table1

azhar does not have rights tolewis.view1 and lewis.table1

Locating View Definition Information

Locating View Definitions

Not available if view was created using WITH ENCRYPTION optionsysobjects: view namesysdepends: base object namessyscomments: view definitionsyscolumns: columns in the viewsp_helptext: provide text used in view definition

Locating View Dependenciessp_depends objectname

Lists objects upon which view depends Lists objects that depend on a view

Hiding View Definitions

Use the WITH ENCRYPTION Option

Do Not Delete Entries in the syscomments Table

USE NorthwindGOCREATE VIEW dbo.[Order Subtotals] WITH ENCRYPTIONASSELECT OrderID, Sum(CONVERT(money,(UnitPrice*Quantity*(1-Discount)/100))*100) AS SubtotalFROM [Order Details]GROUP BY OrderIDGO

USE NorthwindGOCREATE VIEW dbo.[Order Subtotals] WITH ENCRYPTIONASSELECT OrderID, Sum(CONVERT(money,(UnitPrice*Quantity*(1-Discount)/100))*100) AS SubtotalFROM [Order Details]GROUP BY OrderIDGO


Can Affect

Only One Underlying Table Cannot Be Made to

Certain Columns (such as computed columns) Can Cause Errors

If They Affect Columns That Are Not Referenced in the View

Are Verified

If the WITH CHECK OPTION Has Been Specified

Optimizing Performance By Using Views

Performance Considerations

Using Indexed Views

Using Views to Partition Data

Performance Considerations

USE NorthwindGOCREATE VIEW dbo.TopSalesViewASSELECT *FROM dbo.TotalPurchaseViewWHERE Subtotal > 50000GO

USE NorthwindGOCREATE VIEW dbo.TopSalesViewASSELECT *FROM dbo.TotalPurchaseViewWHERE Subtotal > 50000GO

TotalPurchaseTotalPurchaseViewViewTotalPurchaseTotalPurchaseViewView

11 ~~ ~~ ~~ ~~

22 ~~ ~~ ~~ ~~

33 ~~ ~~ ~~ ~~

44 ~~ ~~ ~~ ~~

55 ~~ ~~ ~~ ~~

66 ~~ ~~ ~~ ~~

CustomersCustomersCustomersCustomers

11 ~~ ~~ ~~ nn

22 ~~ ~~ ~~ nn

33 ~~ ~~ ~~ yy

44 ~~ ~~ ~~ yy

55 ~~ ~~ ~~ nn

66 ~~ ~~ ~~ yy

OrdersOrdersOrdersOrders

11 ~~ ~~ ~~ nn

22 ~~ ~~ ~~ nn

33 ~~ ~~ ~~ yy

44 ~~ ~~ ~~ yy

55 ~~ ~~ ~~ nn

66 ~~ ~~ ~~ yy

Order DetailsOrder DetailsOrder DetailsOrder Details

11 ~~ ~~ ~~ ~~

22 ~~ ~~ ~~ ~~

33 ~~ ~~ ~~ ~~

44 ~~ ~~ ~~ ~~

55 ~~ ~~ ~~ ~~

66 ~~ ~~ ~~ ~~

SELECT *FROM dbo.TopSalesViewWHERE CompanyName = 'Ernst Handel'

SELECT *FROM dbo.TopSalesViewWHERE CompanyName = 'Ernst Handel'

TopSalesViewTopSalesViewTopSalesViewTopSalesView

~~ ~~ ~~

~~ ~~ ~~

~~ ~~ ~~

TopSalesView depends on TotalPurchaseView: Any

performance problems in the underlying view can be hidden.

Using Indexed Views

Indexed Views Store the Result Sets in the Database

Creating an Indexed View

Guidelines for Creating Indexed Views

Note: Query optimizer can determine using the access statistic.. let it do that.

Use explicitly when:

Performance gains outweigh maintenance costs

Underlying data is infrequently updated

Queries perform many joins and aggregations

Using Indexed Views

Restrictions on Creating Indexed Views

First index must be UNIQUE CLUSTERED

Create view with SCHEMABINDING option

View cannot reference other views

Using Views to Partition Data

You Can Use Views to Partition Data Across Multiple Servers or Instances of SQL Server

Use UNION to combine multiple tables across servers

How SQL Server Uses Views to Partition Data

Tables can be partitioned on separate servers (or processors) for parallel scanning

How Partitioned Views Improve Performance

Parallel processing

Recommended Practices

dbo Should Own All Viewsdbo Should Own All Views

Verify Object Dependencies Before You Drop ObjectsVerify Object Dependencies Before You Drop Objects

Carefully Evaluate Creating Views Based on ViewsCarefully Evaluate Creating Views Based on Views

Never Delete Entries in the syscomments TableNever Delete Entries in the syscomments Table

Use a Standard Naming ConventionUse a Standard Naming Convention

Review

Introduction to Views

Advantages of Views

Defining Views


Optimizing Performance by Using Views

module 8: implementing views. overview introduction advantages definition modifying data through...

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