1. Views in Oracle 10g
Version 1.0
Rushdi Shams, Dept of CSE, KUET 1

2. What is a View
 View is a virtual table.
 It does not contain any data.
 Views, however, are saved in the
database just like tables.
 So, views are database objects.
 A view is simply a window to a database
and represents a particular perspective
to the user.
Rushdi Shams, Dept of CSE, KUET 2

3. What is a View
 Views are similar to queries in that
respect that they too derive a result table
– which is virtual from the actual base
table.
 The difference between views and
queries is – views can be queried as well!
Rushdi Shams, Dept of CSE, KUET 3

4. Advantage of View
 I said – Views are windows to the
database tables.
 Windows are used to see the outside
world.
 So, is view used to only see the outside
world?
Not at all!
Rushdi Shams, Dept of CSE, KUET 4

5. Advantage of View
 The main point of view is to restrict what
you can see in the underlying database
table by selective columns.
 They can be used to make complex queries
easy. A user can use a simple query on a
view to display data from multiple tables,
without having the knowledge of how to
join tables in queries.
 Different views can be created from the
same data as per the requirements of
different types of use groups.
Rushdi Shams, Dept of CSE, KUET 5

6. Our Table
Rushdi Shams, Dept of CSE, KUET 6
 This is our table. We will play with this table
to understand views.

7. Creating a View
Rushdi Shams, Dept of CSE, KUET 7
 We are now creating a view named test_view
that selects all records of CSD students

8. Querying the View
Rushdi Shams, Dept of CSE, KUET 8
 As we said earlier, we can query a view, we
have selected everything test_view provides.

9. Querying the View
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 In this case, we have filtered the result found
from the view with WHERE clause.

10. View makes Complex Query Simple
Rushdi Shams, Dept of CSE, KUET 10
 In SQL, the query we have made in the
previous slide should look like this.
 Which one is simpler?

11. Creating another View
Rushdi Shams, Dept of CSE, KUET 11
 This time we are creating another view
named test_view_2 which will contain the
records of BSD students.

12. Querying the Second View
Rushdi Shams, Dept of CSE, KUET 12
 Again we have queried the second view and
found appropriate records.

13. Simplicity
 This property is called simplicity
 The student data are for the whole
university
 We have simplified the data so that BSD
people won’t have to bother about CSD
people and vice versa.
Rushdi Shams, Dept of CSE, KUET 13

14. Creating the Third View
Rushdi Shams, Dept of CSE, KUET 14
 test_view_3 is created.
 The third line takes the months between the
current date (sysdate) and the date on birthday
column. Then divides it by 12 to get the year.
Then the whole number is passed as argument
of FLOOR function. That is the age of every
entry in the table.

15. Querying the View
Rushdi Shams, Dept of CSE, KUET 15

16. Functionality
 Another property of views.
 It means that we can provide the user
AGE and the user may never ever be
able to know that there is actually no
column such as AGE. AGE is actually
derived from other columns of the table.
Rushdi Shams, Dept of CSE, KUET 16

17. Security
 It is the third property of views.
 It is an extension of SIMPLICITY
property.
 BSD student records are safe now from
CSD students (As CSD students are
technologically smart )
 Do you think teachers will allow you to
see their salaries?
Rushdi Shams, Dept of CSE, KUET 17

18. Updating through Views
 Now we will take a look into issues we
need to know while updating tables
through views.
Rushdi Shams, Dept of CSE, KUET 18

19. Creating Fourth View
Rushdi Shams, Dept of CSE, KUET 19
 We have created test_view_4 which does not
have all the columns of the table.

20. Querying the View
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21. Our View 1 and View 4
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22. What We can do View 1?
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 we can insert a new row into the view
 delete an existing record from a view
 update an existing field in the view.

23. Problem updating through View 4
 suppose we wished to insert a record for a new
student, F, M, BSD. We would have to insert the
record null, F, M, null, null, BSD into the
underlying students table.
 This attempt will fail since studentNo (the table’s
primary key) must not be null.
23Rushdi Shams, Dept of CSE, KUET

24. To make a View Updatable
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25. Updating through an Updatable
View
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26. Querying the Updated View
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27. Inserting through a Wrong
View
Rushdi Shams, Dept of CSE, KUET 27
 Now, we are trying to enter a student of BSD
through a view (view 1) created for CSD
students.

28. The Result!
Rushdi Shams, Dept of CSE, KUET 28
 The view inserted it into the table but it cannot
be queried with view 1
 You can query it through view 2 (created for
BSD students)

29. The Solution
Rushdi Shams, Dept of CSE, KUET 29
 We have changed the CREATE VIEW statement
for our view 1 by adding WITH CHECK OPTION
 Now we are attempting to insert records for BSD
students through a view created for CSD
students.

30. The Result
Rushdi Shams, Dept of CSE, KUET 30
 Oracle got you!
 You cannot violate that when you have
created the view with a WITH CHECK
OPTION

31. Dropping the Views
Rushdi Shams, Dept of CSE, KUET 31
 Finally, we are dropping all the four views
with DROP VIEW option.

32. References
 Database Systems (Third Edition) by Paul
Beynon-Davies
 Structured Query Language (SQL): A
Practical Introduction by Akil I. Din
 Oracle forums at
http://forums.oracle.com/forums/thread.j
spa?threadID=378783 [21 March 2008]
 Geek Interview at
http://www.geekinterview.com/question_
details/338 [21 March 2008]
Rushdi Shams, Dept of CSE, KUET 32