1 Creating and Managing Views Explained

Key Concepts

1. Definition of Views
2. Creating Views
3. Modifying Views
4. Dropping Views
5. Advantages of Views
6. Types of Views

1. Definition of Views

A view is a virtual table based on the result-set of an SQL statement. It does not store data physically but provides a way to present data from one or more tables in a structured format.

2. Creating Views

Views are created using the CREATE VIEW statement. The view definition includes the SQL query that defines the view.

Example:

CREATE VIEW EmployeeDetails AS
SELECT EmployeeID, FirstName, LastName, Department
FROM Employees
WHERE Department = 'Sales';

This view provides a simplified way to access employee details for the 'Sales' department.

3. Modifying Views

Views can be modified using the ALTER VIEW statement. This allows you to change the definition of an existing view without dropping and recreating it.

Example:

ALTER VIEW EmployeeDetails AS
SELECT EmployeeID, FirstName, LastName, Department, Salary
FROM Employees
WHERE Department = 'Sales';

This modification adds the 'Salary' column to the existing view.

4. Dropping Views

Views can be dropped using the DROP VIEW statement. This removes the view from the database.

Example:

DROP VIEW EmployeeDetails;

This command removes the 'EmployeeDetails' view from the database.

5. Advantages of Views

Views offer several advantages:

• Security: Restrict access to certain columns or rows of a table.
• Simplicity: Simplify complex queries by encapsulating them in a view.
• Consistency: Ensure consistent data presentation across different queries.
• Performance: Optimize query performance by pre-filtering data.

6. Types of Views

There are different types of views:

• Simple Views: Based on a single table with no aggregation functions.
• Complex Views: Based on multiple tables or include aggregation functions.
• Updatable Views: Allow data modifications (INSERT, UPDATE, DELETE) through the view.
• ReadOnly Views: Do not allow data modifications.

Analogies for Clarity

Think of a view as a window through which you can see specific parts of a room. Just as a window filters the view of a room, a view filters and presents specific data from one or more tables.

Insightful Value

Understanding and effectively using views is essential for managing and querying data in a database. By creating and managing views, you can enhance security, simplify complex queries, ensure data consistency, and improve query performance, making your database operations more efficient and robust.