SQL Views

In SQL, a view is a virtual table that is based on the result set of a SQL statement. A view can be thought of as a saved SQL query that can be referenced like a table. When a view is created, the query that defines the view is stored in the database, but the view itself does not contain any data.

Views are useful for a variety of purposes, such as:

• Simplifying complex SQL queries by abstracting away the details of the underlying tables
• Providing a simplified or customized view of data that can be accessed by different users or applications
• Restricting access to sensitive or confidential data by limiting the columns or rows that can be accessed
• Improving query performance by precomputing frequently used queries and storing the results in the view

To create a view in SQL, you can use the CREATE VIEW statement, followed by a SELECT statement that defines the view's query. For example:

CREATE VIEW employee_names AS
SELECT first_name, last_name FROM employees;

This creates a view called employee_names that contains the first_name and last_name columns from the employees table. Once the view is created, it can be queried like any other table:

SELECT * FROM employee_names;

This will return a result set that contains the first_name and last_name columns from the employees table, as defined by the view. Note that any changes made to the underlying tables will be reflected in the view, since the view is based on a query that is executed each time the view is accessed.