SQL - VIEWS

The SQL VIEW statement is used to create a SQL VIEW which is a virtual table created based on the SQL statement. A view contains rows and columns just like a normal table. All SQL functions, WHERE, HAVING and JOINs statements can be used to create a SQL VIEW. The SQL VIEW statement can be used to create, update or delete a view.

Syntax

The syntax for using VIEW statement is given below:

/* Create a view */
CREATE VIEW view_name AS
SELECT column1, column2, column3, ...
FROM table_name
WHERE condition(s);

/* Update a view */
CREATE OR REPLACE VIEW view_name AS
SELECT column1, column2, column3, ...
FROM table_name
WHERE condition(s);

/* Drop a view */
DROP VIEW view_name;

Example:

Consider a database table called Employee with the following records:

CREATE VIEW

The below mentioned SQL statement is used to create a view on Employee table which contains all records of employee whose salary is greater than 2800.

CREATE VIEW Employee_Salary_GT_2800 AS
SELECT * FROM Employee WHERE Salary > 2800;

Query the VIEW

After creating the VIEW, it can be used as mentioned below:

SELECT * FROM Employee_Salary_GT_2800;

This will produce the result as shown below:

CREATE OR REPLACE VIEW

The CREATE OR REPLACE VIEW statement is used to update the view if it exists otherwise creates a new view.

Note: CREATE OR REPLACE VIEW clause is not supported in all database. For example SQL Server supports the CREATE OR ALTER VIEW clause for the same purpose.

The mentioned below statement is used to update the above view which contains all records of employee whose salary is greater than 2800 and age is greater than 25.

/* MySQL / Oracle */
CREATE OR REPLACE VIEW Employee_Salary_GT_2800 AS
SELECT * FROM Employee WHERE Salary > 2800 AND AGE > 25;

/* SQL Server */
CREATE OR ALTER VIEW Employee_Salary_GT_2800 AS
SELECT * FROM Employee WHERE Salary > 2800 AND AGE > 25;

After updating the VIEW, the following query can be used to see its content:

SELECT * FROM Employee_Salary_GT_2800;

This will produce the result as shown below:

DROP VIEW

The DROP VIEW is used to delete a view.

DROP VIEW Employee_Salary_GT_2800;