Creating views in MySQL

Introduction

Views let you save a query as a virtual table. This makes it easier to reuse complex queries without rewriting them.

You want to simplify complex queries for yourself or others.

You need to show only specific columns or rows from a table.

You want to hide sensitive data from some users.

You want to reuse the same query in many places without copying it.

You want to organize data in a way that matches how you think about it.

Syntax

MySQL

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

A view acts like a saved SELECT query you can use like a table.

You can select specific columns and filter rows in the view.

Examples

Creates a view showing only active customers with their id, name, and email.

MySQL

CREATE VIEW active_customers AS
SELECT id, name, email
FROM customers
WHERE status = 'active';

Creates a view listing product IDs and their prices.

MySQL

CREATE VIEW product_prices AS
SELECT product_id, price
FROM products;

Creates a view of orders placed after January 1, 2024.

MySQL

CREATE VIEW recent_orders AS
SELECT order_id, customer_id, order_date
FROM orders
WHERE order_date > '2024-01-01';

Sample Program

This example creates an employees table, inserts data, creates a view for the Sales department, and selects all from that view.

MySQL

CREATE TABLE employees (
  id INT PRIMARY KEY,
  name VARCHAR(50),
  department VARCHAR(50),
  salary INT
);

INSERT INTO employees VALUES
(1, 'Alice', 'Sales', 50000),
(2, 'Bob', 'HR', 45000),
(3, 'Charlie', 'Sales', 55000),
(4, 'Diana', 'IT', 60000);

CREATE VIEW sales_team AS
SELECT id, name, salary
FROM employees
WHERE department = 'Sales';

SELECT * FROM sales_team;

Important Notes

Views do not store data themselves; they show data from the original tables.

If the original table changes, the view shows the updated data automatically.

You can use views to improve security by restricting access to certain data.

Summary

Views save queries as virtual tables for easy reuse.

They help simplify complex data and control what users see.

Creating a view uses the CREATE VIEW statement with a SELECT query.

Practice

1. What is the main purpose of creating a view in MySQL?

easy

A. To delete data from multiple tables at once

B. To save a SELECT query as a virtual table for easy reuse

C. To permanently store data physically in the database

D. To create a backup of the database

Solution

1. Step 1: Understand what a view is

   A view is a virtual table that stores a SELECT query, not data itself.

2. Step 2: Identify the purpose of views

   Views simplify complex queries and allow reuse without storing data physically.

3. Final Answer:

   To save a SELECT query as a virtual table for easy reuse -> Option B

4. Quick Check:

   Views = virtual tables for queries [OK]

Hint: Views store queries, not data, for easy reuse [OK]

Common Mistakes:

• Thinking views store data physically
• Confusing views with backups
• Assuming views delete data

2. Which of the following is the correct syntax to create a view named employee_view showing id and name from employees table?

easy

A. VIEW CREATE employee_view AS SELECT id, name FROM employees;

B. CREATE employee_view VIEW AS SELECT id, name FROM employees;

C. CREATE VIEW employee_view AS SELECT id, name FROM employees;

D. CREATE VIEW employee_view SELECT id, name FROM employees;

Solution

1. Step 1: Recall the correct CREATE VIEW syntax

   The syntax is: CREATE VIEW view_name AS SELECT ...

2. Step 2: Match the syntax with options

   CREATE VIEW employee_view AS SELECT id, name FROM employees; matches the correct syntax exactly.

3. Final Answer:

   CREATE VIEW employee_view AS SELECT id, name FROM employees; -> Option C

4. Quick Check:

   CREATE VIEW ... AS SELECT ... [OK]

Hint: Remember: CREATE VIEW name AS SELECT ... [OK]

Common Mistakes:

• Swapping keywords CREATE and VIEW
• Omitting AS keyword
• Incorrect keyword order

3. Given the table products with columns id, name, and price, what will be the output of SELECT * FROM cheap_products; if cheap_products is created as CREATE VIEW cheap_products AS SELECT id, name FROM products WHERE price < 50;?

medium

A. Only id and name columns of products with price less than 50

B. All columns (id, name, price) of products with price less than 50

C. Only products with price greater than or equal to 50

D. Syntax error because price column is missing in view

Solution

1. Step 1: Analyze the view definition

   The view selects only id and name columns where price is less than 50.

2. Step 2: Understand the SELECT * from the view

   Since the view only has id and name, SELECT * returns only these columns for matching rows.

3. Final Answer:

   Only id and name columns of products with price less than 50 -> Option A

4. Quick Check:

   View columns = selected columns only [OK]

Hint: View shows only columns defined in its SELECT [OK]

Common Mistakes:

• Expecting all original table columns
• Confusing filter condition with columns selected
• Assuming syntax error if columns omitted

4. What is wrong with this statement?
CREATE VIEW sales_view AS SELECT order_id, total FROM orders WHERE;

medium

A. Using SELECT instead of INSERT

B. Missing AS keyword before SELECT

C. Incorrect view name syntax

D. Missing condition after WHERE clause

Solution

1. Step 1: Check the syntax after WHERE

   The WHERE clause must have a condition; here it is empty.

2. Step 2: Confirm other parts are correct

   AS keyword is present, view name is valid, SELECT is correct for views.

3. Final Answer:

   Missing condition after WHERE clause -> Option D

4. Quick Check:

   WHERE requires a condition [OK]

Hint: WHERE must always have a condition [OK]

Common Mistakes:

• Leaving WHERE empty
• Confusing AS placement
• Using wrong SQL command for views

5. You want to create a view active_customers that shows customer id, name, and their total orders from customers and orders tables. Which query correctly creates this view?

hard

A. CREATE VIEW active_customers AS SELECT c.id, c.name, COUNT(o.order_id) AS total_orders FROM customers c LEFT JOIN orders o ON c.id = o.customer_id GROUP BY c.id, c.name;

B. CREATE VIEW active_customers AS SELECT id, name, total_orders FROM customers;

C. CREATE VIEW active_customers AS SELECT c.id, c.name, SUM(o.price) FROM customers c JOIN orders o ON c.id = o.customer_id;

D. CREATE VIEW active_customers AS SELECT c.id, c.name, COUNT(o.order_id) FROM customers c, orders o WHERE c.id = o.customer_id;

Solution

1. Step 1: Understand the requirement

   The view must show customer id, name, and total orders count, including customers with zero orders.

2. Step 2: Analyze each option

   CREATE VIEW active_customers AS SELECT c.id, c.name, COUNT(o.order_id) AS total_orders FROM customers c LEFT JOIN orders o ON c.id = o.customer_id GROUP BY c.id, c.name; uses LEFT JOIN to include all customers and counts orders grouped by customer, which is correct.
   CREATE VIEW active_customers AS SELECT id, name, total_orders FROM customers; misses orders data.
   CREATE VIEW active_customers AS SELECT c.id, c.name, SUM(o.price) FROM customers c JOIN orders o ON c.id = o.customer_id; sums price but misses GROUP BY and alias.
   CREATE VIEW active_customers AS SELECT c.id, c.name, COUNT(o.order_id) FROM customers c, orders o WHERE c.id = o.customer_id; uses implicit join without GROUP BY, causing incorrect aggregation.

3. Final Answer:

   CREATE VIEW active_customers AS SELECT c.id, c.name, COUNT(o.order_id) AS total_orders FROM customers c LEFT JOIN orders o ON c.id = o.customer_id GROUP BY c.id, c.name; -> Option A

4. Quick Check:

   LEFT JOIN + GROUP BY + COUNT = correct aggregation [OK]

Hint: Use LEFT JOIN and GROUP BY to count related rows [OK]

Common Mistakes:

• Forgetting GROUP BY with aggregation
• Using INNER JOIN and missing customers without orders
• Not aliasing aggregated columns