Delete Views in SQL Server

In the area of relational databases, SQL Server is one of the most powerful and popular systems. It is flexible to make possible the development of complex data structures and their manipulation. SQL Server offers a crucial tool for managing data which is Delete Views. They allow users to delete rows from multiple tables through a single view.

This also helps maintain data integrity and ensures consistency across the database. In this article, we'll explore the Delete Views in SQL Server and their examples with the output and explanation.

What are Delete Views?

• Deleting Views also called the Updatable Views, are virtual tables that are created from one or more base tables.
  
• By doing this, users may run DELETE operations on the view, resulting in the base tables below being changed.
  
• Unlike SELECT expressions, which only access data, Delete Views can make alterations to the data they stand for.
  
• Delete Views provide a mechanism for simplifying the deletion process in SQL Server databases.

Set Up an Environment

CREATE TABLE Employee (
    EmployeeID INT PRIMARY KEY,
    FirstName VARCHAR(50),
    LastName VARCHAR(50),
    Department VARCHAR(50)
);

INSERT INTO Employee (EmployeeID, FirstName, LastName, Department)
VALUES
    (1, 'John', 'Doe', 'HR'),
    (2, 'Jane', 'Smith', 'IT'),
    (3, 'Michael', 'Johnson', 'Finance'),
    (4, 'Emily', 'Williams', 'Marketing'),
    (5, 'David', 'Brown', 'IT'),
    (6, 'Emma', 'Jones', 'HR');

Output:

| EmployeeID | FirstName | LastName | Department |
|------------|-----------|----------|------------|
|      1     |   John    |   Doe    |     HR     |
|      2     |   Jane    |   Smith  |     IT     |
|      3     |  Michael  |  Johnson |  Finance   |
|      4     |   Emily   | Williams | Marketing  |
|      5     |   David   |   Brown  |     IT     |
|      6     |   Emma    |   Jones  |     HR     |

Create View

Let's create a view name DeleteViewIT based on the Employee table.

-- Delete View 1: Employees in IT department
CREATE VIEW DeleteViewIT
AS
SELECT * FROM Employee
WHERE Department = 'IT'

Output:

| EmployeeID | FirstName | LastName | Department |
|------------|-----------|----------|------------|
|      2     |   Jane    |   Smith  |     IT     |
|      5     |   David   |   Brown  |     IT     |

Let's create a another view name DeleteViewHR based on the Employee table.

-- Delete View 2: Employees in HR department
CREATE VIEW DeleteViewHR
AS
SELECT * FROM Employee
WHERE Department = 'HR'

Output:

| EmployeeID | FirstName | LastName | Department |
|------------|-----------|----------|------------|
|      1     |   John    |   Doe    |     HR     |
|      6     |   Emma    |   Jones  |     HR     |

Delete a View

Let's delete a view name DeleteViewIT based on the Employee table.

DELETE FROM DeleteViewIT;

Output:

| EmployeeID | FirstName | LastName | Department |
|------------|-----------|----------|------------|
|      1     |   John    |   Doe    |     HR     |
|      3     |  Michael  |  Johnson |  Finance   |
|      4     |   Emily   | Williams | Marketing  |
|      6     |   Emma    |  Jones   |     HR     |

Explanation: It will delete all rows from the Employee table where the Department column equals 'IT'.

Let's delete a view name DeleteViewHR based on the Employee table.

DELETE FROM DeleteViewHR;

Output:

| EmployeeID | FirstName | LastName | Department |
|------------|-----------|----------|------------|
|      2     |   Jane    |   Smith  |     IT     |
|      3     |  Michael  |  Johnson |  Finance   |
|      4     |   Emily   | Williams | Marketing  |
|      5     |   David   |   Brown  |     IT     |

Explanation: Rows with EmployeeID 1 (John) and 6 (Emma), who belong to the HR department, have been deleted from the Employee table

Advantages of Delete Views

• Simplified Data Management: Delete Views are the way to delete data from multiple tables without the necessity to execute separate DELETE commands for each table.
  
• Enhanced Data Integrity: The Delete Views locate the complicated delete logic within the view and keep the data integrity by making the related data deletion consistent.
  
• Improved Performance: Sometimes it will be more convenient to use Delete View instead of executing several Delete statements that include complex joins or conditions.
  
• Security: With Delete Views, the users can be allowed to perform delete operations through the view while their direct access to the base tables is restricted.

Conclusion

With the Views deletion in SQL Server you can handle the data deletion operations more effectively and ensure the data consistency. Through view implementation which embeds delete logic into it, developers can make complex deletion tasks simple and get consistent results from the database. Nonetheless, one should take into account the particulars of Delete Views and apply the approach correctly in order to apply the advantages adequately.