Oracle Tutorial - Views

Introduction to Views in Oracle

Views in Oracle are virtual tables that are derived from one or more tables or other views. They provide a way to present data in a customized manner without storing the data physically. Views can simplify complex queries, provide data security, and encapsulate business logic.

Creating Views

To create a view in Oracle, you use the CREATE VIEW statement:

CREATE VIEW EmployeeDetails AS
SELECT EmployeeID, FirstName, LastName, Department
FROM Employees
WHERE Department = 'IT';
                

In this example, EmployeeDetails is the name of the view, and it selects specific columns from the Employees table where the department is IT.

Querying Views

Once created, views can be queried like tables:

SELECT * FROM EmployeeDetails;
                

Updating Views

Views can be updated under certain conditions in Oracle:

UPDATE EmployeeDetails
SET Department = 'HR'
WHERE EmployeeID = 101;
                

Note that complex views with joins or aggregation may have restrictions on updates.

Modifying Views

You can modify the definition of an existing view using the CREATE OR REPLACE VIEW statement:

CREATE OR REPLACE VIEW EmployeeDetails AS
SELECT EmployeeID, FirstName, LastName, Department, Salary
FROM Employees;
                

Dropping Views

To remove a view from the database, use the DROP VIEW statement:

DROP VIEW EmployeeDetails;
                

Advantages of Using Views

• Enhance security by restricting access to specific columns or rows of data.
• Simplify complex queries by encapsulating joins and aggregations.
• Provide a logical layer for applications, shielding them from underlying schema changes.

Conclusion

Views are powerful tools in Oracle that simplify data access and enhance data security by presenting customized virtual tables. By understanding how to create, query, update, and manage views, you can effectively leverage them to improve database management and application development.