A SQL view is a virtual table created by selecting fields from existing tables. Views simplify complex queries, enhance security by controlling data access, and provide a convenient way to represent data. Views cannot modify data or contain ORDER BY clauses without LIMIT. To create a view, use the CREATE VIEW statement followed by a SELECT on the desired fields and tables. Views retrieve data without direct access to tables, abstracting complexity but adding some performance overhead and limiting functionality compared to tables.

1. SQL View
DSE003 – DATABASE MANAGEMENT SYSTEM
HASANKA WIJESINGHE M I T , B . S c

2. What is SQL View?
 A virtual table created by a query by selecting fields
from one or more existing tables.
 Simplifies complex queries, enhances security, and
provides a convenient way to represent data.

4. Restrictions When Creating a View
Views cannot have ORDER BY clauses unless using the
LIMIT clause.
Views cannot contain subqueries in the FROM clause.

6. Restrictions When Creating a View
Views cannot have ORDER BY clauses unless using the
LIMIT clause.
Views cannot contain subqueries in the FROM clause.
Views cannot modify data (no INSERT, UPDATE, or DELETE
operations).

7. Syntax for Creating a View
CREATE VIEW view_name AS
SELECT column1, column2, ...
FROM table_name
WHERE condition;

8. Syntax for Creating a View (Example)
CREATE VIEW employee_view AS
SELECT employee_id, first_name, last_name
FROM employees
WHERE department_id = 1;

9. Retrieve crated view
Syntax:
SELECT * FROM [view name];
Example:
SELECT * FROM employee_view;

10. Advantages of Using View
Simplifies Complex Queries: Abstracts complex joins and
calculations.
Enhances Security: Limits direct access to tables, providing
controlled data access.
Improves Performance: Can optimize and cache query
results.
Data Abstraction: Presents data in a way that makes sense
to users, hiding complexity.

11. Disadvantages of Using View
Performance Overhead: Views might impact performance,
especially with large datasets.
Limited Functionality: Restrictions on operations (no
modifications) limit their use.
Dependency: Changes in underlying tables might affect
views, requiring adjustments.
Complexity: Managing multiple views can become
complex, especially in large databases.

12. Exercise
Use companyDB:
1. Create a view to retrieve the department name with the
manager’s name and the manager's appointed date.
2. Create a view to retrieve dependent details with
employee name.

13. Hasanka Wijesinghe 13
Q & A

14. Hasanka Wijesinghe 14
Thank You!