Modifying and Deleting Views

In SQL, a view is a virtual table based on the result-set of an SQL statement. It contains rows and columns, just like a real table. The fields in a view are fields from one or more real tables in the database. In this tutorial, we will learn how to modify and delete views in SQL.

Modifying a View

The SQL CREATE OR REPLACE VIEW statement is used to modify an existing view. The syntax for modifying a view in SQL is:

CREATE OR REPLACE VIEW view_name AS
SELECT column1, column2, ...
FROM table_name
WHERE condition;

In the code above, the CREATE OR REPLACE VIEW statement will create a new view if it does not exist, or replace an existing view if it exists.

Example

Let's say we have a view named CustomerView that was created from the Customers table. The view was created with the following SQL statement:

CREATE VIEW CustomerView AS
SELECT customerName, contactName
FROM Customers;

Now, suppose we want to modify CustomerView to also include the country field. We can modify the view using the CREATE OR REPLACE VIEW statement like this:

CREATE OR REPLACE VIEW CustomerView AS
SELECT customerName, contactName, country
FROM Customers;

Deleting a View

The SQL DROP VIEW statement is used to delete an existing view. The syntax for deleting a view in SQL is:

DROP VIEW view_name;

In the code above, the DROP VIEW statement deletes the existing view named view_name.

Example

Let's say we want to delete the CustomerView we created earlier. We can delete the view using the DROP VIEW statement like this:

DROP VIEW CustomerView;

This will delete the CustomerView from the database.

Summary

In this tutorial, you learned how to modify and delete views in SQL. The CREATE OR REPLACE VIEW statement is used to modify an existing view and the DROP VIEW statement is used to delete an existing view. Keep practicing these commands to become more comfortable with managing views in SQL.

Remember, views are a powerful feature in SQL as they allow you to save SQL queries and reuse them. However, as with any powerful tool, they should be used with care. Always verify your changes by selecting data from your view to ensure it shows the expected results.