8/2/2019 View-Dsil

1/16

What is VIEW

Logically represents subsets of data from one or more tables

A view is a DBO that consists of columns from one or more tables.

It is a query stored as an object.

View can be referred like any other table in a database.

A view serves as a security mechanism. This ensures that users are ableto retrieve and modify only the data seen by them

8/2/2019 View-Dsil

2/16

Advantages of VIEW

To restrict

data access

To make complex

queries easy

To provide dataindependence

To present differentviews of the same

data

8/2/2019 View-Dsil

3/16

User Defined Views

User Defined Views

Simple View

Complex View

Indexed View

8/2/2019 View-Dsil

4/16

User Defined View

These Views are created by a user as per

requirements.

Simple Views and Complex Views

8/2/2019 View-Dsil

5/16

Creating a View

CREATE VIEW View_Name [(Column List)]

[with {ENCRYPTION |SCHEMABINDING | VIEWMETADAT}]

AS Select

[WITH CHECK OPTION]

8/2/2019 View-Dsil

6/16

Example : Simple View

Create the EMPVDEPT10 view, which contains

details of employees in department 10

CREATE VIEW EMPVDEPT10 ASSELECT Eno,EmpName,Salary,DeptNo

FROM employees

WHERE DeptNo = 10

8/2/2019 View-Dsil

7/16

Example: Complex View

Create a complex view that contains group functions to displayvalues from two tables

CREATE VIEW EMPV(Ename, Minsal, Maxsal, Avgsal)AS SELECT d.DeptName,MIN(e.salary),MAX(e.salary),AVG(e.salary)

FROM employees e JOIN Departments dON (e.DeptNo = d.DeptId)GROUP BY d.DeptName

8/2/2019 View-Dsil

8/16

Rules for Performing

Insert Operations on a View

You cannot add data through a view if the

view includes:

Group functions

A GROUP BY clause The DISTINCT keyword

The pseudocolumn ROWNUM keyword

Columns defined by expressions NOT NULL columns in the base tables that are

not selected by the view

8/2/2019 View-Dsil

9/16

Querying a View

8/2/2019 View-Dsil

10/16

Rules for Performing

Update Operations on a View

You cannot modify data in a view if it contains:

Group functions

A GROUP BY clause

The DISTINCT keyword

The pseudo column ROWNUM keyword

Columns defined by expressions

8/2/2019 View-Dsil

11/16

Rules for Performing

Delete Operations on a View

You can usually perform DML operations

on simple views.

You cannot remove a row if the view contains the

following: Group functions

A GROUP BY clause

The DISTINCT keyword

The pseudocolumn ROWNUM keyword

8/2/2019 View-Dsil

12/16

Using the WITH CHECK OPTION

Clause

You can ensure that DML operations performed onthe view stay in the domain of the view by using theWITH CHECK OPTION clause:

CREATE OR REPLACE VIEW empvu20

AS SELECT *FROM employeesWHERE department_id = 20WITH CHECK OPTION CONSTRAINT

empvu20_ck Any attempt to change the department number for

any row in the view fails because it violates the WITHCHECK OPTION constraint.

8/2/2019 View-Dsil

13/16

WITH Encryption

The WITH ENCRYPTION option encrypts the

SELECT statement, thus enhancing the security

of the database system. Software vendors who

use SQL Server in the back end often encrypt

their views or stored procedures in order to

prevent tampering or reverse-engineering from

clients or competitors. If you use encryption, besure to save the original, unencrypted definition.

8/2/2019 View-Dsil

14/16

WITH SCHEMABINDING

The SCHEMABINDING clause binds the view to

the schema of the underlying table. Creating a

view with the SCHEMABINDING option locks

the tables being referred by the view and

prevents any changes that may change the

table schema.

8/2/2019 View-Dsil

15/16

Drop View

You can remove a view without losing data

because a view is based on underlying tables

in the database.

DROP VIEWview;

DROP VIEW empvu80;

ALTER VIEW "Alphabetical list of products" AS

SELECT Statement

8/2/2019 View-Dsil

16/16

Indexed View

A view created with a unique clustered index is known as an Indexed View orMaterialized View. Unlike views, an Indexed View exists on the disk like a table inwhich the clustered index is created. Once a clustered index is created you maycreate non-clustered indexes on the view

CREATE VIEW vwOrderDetails WITH SCHEMABINDING

AS

SELECT OD.OrderID, OD.ProductID, P.ProductName , OD.UnitPrice , OD.Quantity, OD.Discount

FROM dbo.Products P

INNER JOIN dbo.[Order Details] OD

ON P.ProductID = OD.ProductID

GO

SET QUOTED_IDENTIFIER ON SET ANSI_NULLS ON

GO

CREATE UNIQUE CLUSTERED INDEX [IDX_vwOrderDetails]