Creating Views

Introduction

A view in SQL 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. A view can be considered as a pre-written SQL query stored in the database itself.

Why Use Views?

1. Simplicity: Views provide a simple way to represent complex queries. They allow you to save a complex query and then simply refer to it like you would a table.
2. Security: Views can limit the degree of exposure of the underlying tables to the outer world. They can encapsulate the name and schema of underlying tables.
3. Data Integrity: If data is accessed and entered through a view, the DBMS can automatically check the data to ensure that it meets the specified integrity constraints.

Creating a View

Creating a view in SQL is done using the CREATE VIEW statement. The syntax is as follows:

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

Here, view_name is the name of the view you want to create, column1, column2, ... are the names of the columns you want to include in your view, table_name is the name of the table these columns are from, and condition is a filter applied to the data, just as you would in a WHERE statement in a regular query.

For example, let's say we have a table named Customers with the following data:

CustomerID	Name	ContactNumber
1	John	1234567890
2	Alice	2345678901
3	Bob	3456789012

We can create a view that only shows the Name and ContactNumber columns as follows:

CREATE VIEW CustomerContacts AS
SELECT Name, ContactNumber
FROM Customers;

Now, if you run a SELECT * FROM CustomerContacts;, it will return:

Name	ContactNumber
John	1234567890
Alice	2345678901
Bob	3456789012

Updating a View

You can update a view using the CREATE OR REPLACE VIEW statement. The syntax is as follows:

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

This will update the view to include the new columns or conditions you specify.

Deleting a View

You can delete a view using the DROP VIEW statement. The syntax is as follows:

DROP VIEW view_name;

This will permanently delete the view from your database.

Conclusion

Views in SQL are a powerful feature that can simplify complex queries, increase security, and ensure data integrity. They are easy to create, update, and delete, making them a great tool for any SQL user.