Module 11 Implementing Views

8/9/2019 Module 11 Implementing Views

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Overview

Introduction to Views

Advantages of Views

Defining Views

Modifying Data Through Views




A View is a Virtual Table which consists of a subset of columns fromone or more tables.

i.e. View is an object that derives its data from one or more tables( Base tables or Underlying Tables).

A View is a Named Table that is represented, not by its own physicallystored data, but by its definition in terms of other named tables( Base Tables).

View is a “ Virtual table”, deriving its data from “ Base Tables”



Creating a View

EmployeeView

EmployeeView EmployeeView

Lastname

Lastname Firstname

Firstname

Davolio

Fuller

Leverling

Davolio

Fuller

Leverling

Nancy

Andrew

Janet

Nancy

Andrew

Janet

Employees

Employees Employees

EmployeeID

EmployeeID LastName

LastName Firstname

Firstname Title

Title

1

2

3

1

2

3

Davolio

Fuller

Leverling

Davolio

Fuller

Leverling

Nancy

Andrew

Janet

Nancy

Andrew

Janet

~~~

~~~

~~~

~~~

~~~

~~~

UserUser’’s Views View

USE NorthwindGOCREATE VIEW EmployeeViewAS

SELECT LastName, FirstnameFROM Employees

USE NorthwindGOCREATE VIEW 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

Mask Database Complexity

Hide complex database design

Simplify complex queries

Simplify Management of User Permissions

Improve Performance



Example: View of Joined Tables

OrderID

OrderIDOrderID

1066310827104271045110515

1066310827104271045110515

CustomerID

CustomerIDCustomerID

BONAPBONAPPICCOQUICKQUICK

BONAPBONAPPICCOQUICKQUICK

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

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

RequiredDate

RequiredDateRequiredDate

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

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

ShippedDate

ShippedDateShippedDate

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 Northwind

GO

CREATE VIEW ShipStatusViewAS

SELECT OrderID, RequiredDate, ShippedDate,ContactName

FROM Customers c INNER JOIN Orders o

ON c.CustomerID = O.CustomerIDWHERE RequiredDate < ShippedDate

USE NorthwindGO

CREATE VIEW ShipStatusView

AS

SELECT OrderID, RequiredDate, ShippedDate,ContactName

FROM Customers c INNER JOIN Orders o

ON c.CustomerID = O.CustomerIDWHERE RequiredDate < ShippedDate

CustomerID

CustomerIDCustomerID

BONAPPICCOQUICK

BONAPPICCOQUICK

CompanyName

CompanyNameCompanyName

Bon app'Piccolo und mehr QUICK-Stop

Bon app'Piccolo und mehr QUICK-Stop

ContactName

ContactNameContactName

Laurence LebihanGeorg PippsHorst Kloss


OrderID

OrderIDOrderID

102641027110280

102641027110280

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

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

ShippedDate

ShippedDateShippedDate

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

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

ContactName

ContactNameContactName





Altering and Dropping Views

Altering Views

Retains assigned permissions

Causes new SELECT statement and options to replace

existing definition Dropping Views

USE NorthwindGOALTER VIEW EmployeeViewASSELECT LastName, FirstName, ExtensionFROM Employees

USE NorthwindGOALTER VIEW EmployeeViewAS

SELECT LastName, FirstName, ExtensionFROM Employees

DROP VIEW ShipStatusViewDROP VIEW ShipStatusView



Locating View Definition Information

Locating View Definitions

Sp_helptext ‘View_Name’

Locating View Dependencies

Lists objects upon which view depends

Lists objects that depend on a view

Sp_depends ‘View_Name’



Hiding View Definitions

Use the WITH ENCRYPTION Option

USE NorthwindGOCREATE VIEW customers_view

WITH ENCRYPTION

ASSELECT customerid,companyname

FROM customersGO

USE NorthwindGOCREATE VIEW customers_view

WITH ENCRYPTION

ASSELECT customerid,companynameFROM customers

GO

Sp_helptext ‘customers_view’The object comments have been encrypted.




Cannot Affect More Than One Underlying Table

Cannot Be Made to Certain Columns

Can Cause Errors If They Affect Columns That Are NotReferenced in the View

Are Verified If the WITH CHECK OPTION Has BeenSpecified



With check Option

CREATE VIEW svc

WITH ENCRYPTIONas select * from student

where age between 18 and 20

WITH CHECK OPTION



With Check Option

By default, as rows are added or updated through a view, they disappear from the scope of the view when they no longer fall into the criteria of thequery defining the view.

For example, a query can be created, defining a view that retrieves allrows from a table where the employee's salary is less than $30,000. If the employee's salary is increased to $32,000, then querying the view no

longer displays that particular employee because his or her salary doesnot conform to the criteria set by the view.

However, the WITH CHECK OPTION clause forces all data modificationstatements executed against the view to adhere to the criteria set withinthe SELECT statement defining the view. If you use this clause, rowscannot be modified in a way that causes them to disappear from the

view. Any modification that would cause this to happen is canceled andan error is displayed.



With Check Option

insert into svc

values('1111119','abc','Male',21,'Delhi')

Server: Msg 550, Level 16, State 1, Line 1

The attempted insert or update failed because the target view either

specifies WITH CHECK OPTION or spans a view that specifies

WITH CHECK OPTION and one or more rows resulting from the

operation did not qualify under the CHECK OPTION constraint.

The statement has been terminated.



Check Your Understanding.



Q.1 What is View.?



Q.2. What is Base Table. ?



Q.3. What are the advantages of a View.?



Q.4.Views are not autonomous and do not exist by their own right.?

1. True

2. False



Q.5. What is the Syntax to create a View.



Q.6. What is With Encryption.?



Q.7. What is With Check Option.



Q.8. The View created by using With Encryption can beDecrypted .?

1. Yes

2. No



Q.9. Views can be used for ________

1. Providing row and column level security.

2. Ensuring efficient access to data.

3. Masking data complexity from user.

4. Helps to work as Physical Table for User.

5. All of the Above.



Q.10. If columns names are not specified explicitly in theView Definition statement then the view inherits thecolumn names of the______________

1. System catalog

2. Sp_depends

3. Source of the View

4. None of the above.



Q.11. The Clause ‘ WITH CHECK OPTION ’ indicates thatUpdate and Insert operations against the view are tobe checked to ensure that the Updated or Inserted

rows dissatisfy the view definition condition.

1. True

2. False



Q.12. You are executing performance optimization onyour company's market research database. On thetblConsumers table, you have a view namedvConsumerData. You would like to see the originalstatement used to create the view. What statement

should you execute?1. sp_helptext vConsumerData

2. sp_helptext tbl_Consumers

3. sp_depends v_ConsumerData

4. sp_depends tbl_Consumers



Q.13. Which of the following statements is true aboutmodifying data using a view?

1. The data from multiple underlying tables can bemodified simultaneously.

2. Changes can be made to computed columns.

3. The view cannot be defined on a single table.

4. Modifications to data in a view affect the base table.



Review


Advantages of Views

Defining Views




It isCourage and Character

that is the deadly combinationfor Success

Thank You.

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Module 11 Implementing Views