3.5 Views

 Views in SQL Server are virtual tables that are based on the result of a SELECT query. They provide a way to simplify complex queries and encapsulate the underlying table structures. This tutorial will guide you through the creation, modification, and usage of views in SQL Server.

3.5.1 Creating Views

To create a view, use the CREATE VIEW statement followed by the view name and the SELECT query defining the view's structure.

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

Let's create a simple view:

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

3.5.2 Modifying Views

Views can be modified using the ALTER VIEW statement. You can add, remove, or modify columns, as well as redefine the SELECT query.

sql
ALTER VIEW [view_name] AS
SELECT new_column1, new_column2, ...
FROM new_table
WHERE new_condition;

Example:

sql
ALTER VIEW EmployeeView AS
SELECT EmployeeID, FirstName, LastName, Salary
FROM Employees
WHERE Department = 'IT';

3.5.3 Querying Views

Once created, views can be queried just like tables. Use the SELECT statement to retrieve data from a view.

sql
SELECT * FROM EmployeeView;

You can join views with other tables or views to create more complex queries:

sql
SELECT EmployeeView.EmployeeID, EmployeeView.FirstName, EmployeeView.LastName, Department.DepartmentName
FROM EmployeeView
INNER JOIN Department ON EmployeeView.DepartmentID = Department.DepartmentID;

3.5.4 Indexing Views

Views themselves do not store data; they retrieve data dynamically from the underlying tables. However, you can create an index on a view to improve query performance.

sql
-- Create an index on a view
CREATE INDEX IX_EmployeeView_DepartmentID
ON EmployeeView (DepartmentID);

3.5.5 Dropping Views

To remove a view, use the DROP VIEW statement:

sql
DROP VIEW [view_name];

Be cautious when dropping views, as it will permanently remove the view and its definition.

sql
DROP VIEW EmployeeView;

Conclusion

Views are powerful tools in SQL Server for simplifying queries, enhancing security, and providing a layer of abstraction over the underlying database structure. By mastering views, you can efficiently manage and manipulate data in your SQL Server databases.