Objectivesj i

After completing this lesson, you should be able to do the following:

•• Describeri a viewi

•• Creater te a viewi

•• Retrievetri datata throught r a viewi

•• Alterlt r thet definitionfi iti off a viewi

•• Insert,I rt, update,t , and deletel te datata throught r a viewi

•• Dropr a viewi

12-2

Database Objectsj

12-3

What IsIs a View?i

EMP Table

12-4

Why Use Views?i

•• To restrictr tri t databaset access

•• To make complexl queriesri easy

•• To allowll datata independencei

•• To presentr t differentiff r t viewsi off thet same datata

12-5

Simplei le Viewsi and Complexl Viewsi

12-6

Creatingi a Viewi

•You embed a subquery within the CREATE VIEW statement.

•You embed a subquery within the CREATE VIEW statement.

•The subquery can contain complex SELECT syntax.

•The subquery can contain complex SELECT syntax.

•The subquery cannot contain an ORDER BY clause.

•The subquery cannot contain an ORDER BY clause.

CREATE [OR REPLACE] [FORCE|NOFORCE] VIEW view

[(alias[, alias]...)] AS subquery

[WITH CHECK OPTION [CONSTRAINT constraint]]

[WITH READ ONLY]

12-7

Creatingi a Viewi

•• Creater te a view,i , EMPVU10,, thatt t containst i detailst ils off employeesl inin departmentrt t 10..

•• Describeri thet structuretr t re off thet viewi by usingi thet SQL*Plus* l DESCRIBEI command..

SQL> DESCRIBE empvu10

12-8

Creatingi a Viewi

•• Creater te a viewi by usingi columnl aliasesli inin thet subqueryry..

•• Selectl t thet columnsl fromfr thist is viewi by thet giveni aliasli names..

12-9

Retrievingi i Data from a Viewi

12-10

Queryingi a Viewi

12-11