← Back to Curriculum

MySQL Views

📚 Lesson 7 of 15 ⏱️ 30 min

MySQL Views

30 min

MySQL views are virtual tables based on the result set of a SELECT statement. Views don't store data themselves but provide a way to present data from underlying tables in a different structure. Views can simplify complex queries, provide data abstraction, control access to sensitive data, and present consistent interfaces to applications. Understanding views enables you to build flexible, maintainable database schemas.

Views are created using CREATE VIEW with a view name and a SELECT statement. Views can be queried like regular tables using SELECT statements. Views can join multiple tables, apply filters, perform calculations, and present data in any structure needed. Views are updated automatically when underlying table data changes. Understanding view creation enables you to create useful data abstractions.

Views can be used for security by restricting access to specific columns or rows. Instead of granting direct table access, you can grant access to views that expose only the necessary data. Views can filter rows based on user context or hide sensitive columns. Understanding views for security enables fine-grained access control.

Views simplify complex queries by encapsulating joins, calculations, and filters. Applications can query views instead of writing complex SQL, reducing code complexity and improving maintainability. Views can be updated when business requirements change without modifying application code. Understanding views for simplification enables cleaner application code.

Materialized views (not natively supported in MySQL but can be simulated) store pre-computed results for faster access. Regular views execute their underlying query each time they're accessed, while materialized views store results that must be refreshed. Understanding the difference enables you to choose appropriate views for performance requirements.

Best practices for views include keeping view definitions simple, documenting view purposes, avoiding deeply nested views, and understanding performance implications. Views can impact performance if they involve complex queries or large datasets. Understanding best practices enables effective view usage.

Key Concepts

  • Views are virtual tables based on SELECT statements.
  • Views don't store data but present data from underlying tables.
  • Views can simplify complex queries and provide data abstraction.
  • Views can be used for security by restricting data access.
  • Views are updated automatically when underlying data changes.

Learning Objectives

Master

  • Creating views for query simplification
  • Using views for data abstraction and security
  • Understanding view limitations and performance
  • Managing and updating views

Develop

  • Understanding database abstraction patterns
  • Designing maintainable database interfaces
  • Implementing security through views

Tips

  • Create view: CREATE VIEW view_name AS SELECT ... FROM table WHERE ...
  • Query views: SELECT * FROM view_name WHERE ... (like regular tables).
  • Update view: ALTER VIEW view_name AS SELECT ... (new definition).
  • Drop view: DROP VIEW view_name to remove a view.

Common Pitfalls

  • Creating overly complex views, causing performance issues.
  • Not understanding view limitations, expecting views to behave like tables.
  • Creating deeply nested views, reducing readability and performance.
  • Not documenting views, making maintenance difficult.

Summary

  • Views provide virtual tables based on SELECT statements.
  • Views simplify queries and provide data abstraction.
  • Views can be used for security and access control.
  • Understanding views enables flexible database design.

Exercise

Create views for common query patterns and data abstraction.

-- Create a view for active products
CREATE VIEW active_products AS
SELECT id, name, price, category, stock
FROM products
WHERE is_active = TRUE AND stock > 0;

-- Create a view for user order summary
CREATE VIEW user_order_summary AS
SELECT 
    u.id,
    u.name,
    u.email,
    COUNT(o.id) as total_orders,
    SUM(o.total_amount) as total_spent,
    MAX(o.order_date) as last_order_date
FROM users u
LEFT JOIN orders o ON u.id = o.user_id AND o.status = 'completed'
GROUP BY u.id, u.name, u.email;

-- Create a view for product sales
CREATE VIEW product_sales AS
SELECT 
    p.id,
    p.name,
    p.category,
    SUM(oi.quantity) as total_sold,
    SUM(oi.quantity * oi.unit_price) as total_revenue
FROM products p
LEFT JOIN order_items oi ON p.id = oi.product_id
LEFT JOIN orders o ON oi.order_id = o.id AND o.status = 'completed'
GROUP BY p.id, p.name, p.category;

-- Use the views
SELECT * FROM active_products WHERE category = 'electronics';
SELECT * FROM user_order_summary WHERE total_spent > 100;
SELECT * FROM product_sales ORDER BY total_revenue DESC;

Exercise Tips

  • Use views to simplify complex joins: encapsulate multi-table queries.
  • Create views for common queries: reduce code duplication.
  • Use views for security: grant access to views instead of tables.
  • Update views when requirements change: ALTER VIEW to modify definitions.

Code Editor

Output