developer-roadmap/src/data/courses/sql-mastery/chapters/subqueries-and-ctes/lessons/books-above-average.md

title	description	order	type	setup
Books Above Average	Practice using simple subqueries to find books above average price	141	challenge	```sql CREATE TABLE book ( id INT PRIMARY KEY, title VARCHAR(100), category VARCHAR(50), price DECIMAL(10,2), stock INT ); INSERT INTO book (id, title, category, price, stock) VALUES (1, 'SQL Basics', 'Programming', 29.99, 10), (2, 'Advanced SQL', 'Programming', 49.99, 5), (3, 'Data Science', 'Data Analysis', 39.99, 8), (4, 'Web Development', 'Programming', 34.99, 12), (5, 'Statistics 101', 'Data Analysis', 24.99, 15), (6, 'Machine Learning', 'Data Analysis', 44.99, 6); ```

The bookstore manager wants to identify expensive books that might need a price adjustment. They need to find all books that are priced above the average book price.

Given the following data in table book:

id	title	category	price	stock
1	SQL Basics	Programming	29.99	10
2	Advanced SQL	Programming	49.99	5
3	Data Science	Data Analysis	39.99	8
4	Web Development	Programming	34.99	12
5	Statistics 101	Data Analysis	24.99	15
6	Machine Learning	Data Analysis	44.99	6

Write a query that shows:

• Book title
• Category
• Price
• How much the price is above the average (rounded to 2 decimal places)

Only include books that are priced above the average book price.

Expected Output

title	category	price	above_average
Advanced SQL	Programming	49.99	12.66
Machine Learning	Data Analysis	44.99	7.66
Data Science	Data Analysis	39.99	2.66

Note: The average book price is 37.33

Solution

SELECT 
    title,
    category,
    price,
    ROUND(price - (
        SELECT AVG(price)
        FROM book
    ), 2) as above_average
FROM book
WHERE price > (
    SELECT AVG(price)
    FROM book
)
ORDER BY price DESC;

This challenge requires you to:

1. Calculate the average price using a subquery
2. Compare each book's price to this average
3. Show how much each book is above the average price

The solution demonstrates the use of subqueries:

• In the SELECT clause to calculate the difference from average
• In the WHERE clause to filter for above-average prices

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