developer-roadmap/src/data/courses/sql-mastery/chapters/aggregate-functions/lessons/publisher-stats.md

title	description	order	type	setup
Publisher Stats	Practice basic aggregation with publisher data	96	challenge	```sql CREATE TABLE publisher ( id INT PRIMARY KEY, name VARCHAR(255), country VARCHAR(100) ); CREATE TABLE book ( id INT PRIMARY KEY, title VARCHAR(255), publisher_id INT, pages INT, stock_level INT, price DECIMAL(10,2) ); INSERT INTO publisher (id, name, country) VALUES (1, 'Tech Books Inc', 'USA'), (2, 'Global Publishing', 'UK'), (3, 'Education Press', 'Canada'), (4, 'Digital Media Ltd', 'Australia'); INSERT INTO book (id, title, publisher_id, pages, stock_level, price) VALUES (1, 'Database Fundamentals', 1, 300, 25, 29.99), (2, 'Advanced SQL', 1, 400, 15, 39.99), (3, 'Web Development', 1, 350, 0, 34.99), (4, 'Python Mastery', 2, 450, 30, 44.99), (5, 'Cloud Computing', 2, 375, 5, 49.99), (6, 'Data Science', 3, 425, 20, 54.99), (7, 'Machine Learning', 3, 500, 12, 59.99), (8, 'Cybersecurity', 4, 350, 8, 45.99); ```

The bookstore wants to analyze their publishers' performance in terms of book variety, pricing, and stock levels.

Given the following data in table publisher:

id	name	country
1	Tech Books Inc	USA
2	Global Publishing	UK
3	Education Press	Canada
4	Digital Media Ltd	Australia

And the following data in table book:

id	title	publisher_id	pages	stock_level	price
1	Database Fundamentals	1	300	25	29.99
2	Advanced SQL	1	400	15	39.99
3	Web Development	1	350	0	34.99
4	Python Mastery	2	450	30	44.99
5	Cloud Computing	2	375	5	49.99
6	Data Science	3	425	20	54.99
7	Machine Learning	3	500	12	59.99
8	Cybersecurity	4	350	8	45.99

Write a query that shows for each publisher:

• Publisher name
• Number of books published
• Total books in stock
• Average book price
• Number of out-of-stock books (stock_level = 0)

Only include publishers who have published at least one book, and order the results by number of books in descending order.

Expected Output

publisher_name	book_count	total_stock	avg_price	out_of_stock
Tech Books Inc	3	40	34.99	1
Global Publishing	2	35	47.49	0
Education Press	2	32	57.49	0
Digital Media Ltd	1	8	45.99	0

Solution

SELECT 
    p.name as publisher_name,
    COUNT(*) as book_count,
    SUM(b.stock_level) as total_stock,
    AVG(b.price) as avg_price,
    COUNT(CASE WHEN b.stock_level = 0 THEN 1 END) as out_of_stock
FROM publisher p
INNER JOIN book b ON p.id = b.publisher_id
GROUP BY p.id, p.name
ORDER BY book_count DESC;

Explanation

Let's break down how this query works:

We join the publisher and book tables:

FROM publisher p
INNER JOIN book b ON p.id = b.publisher_id

We calculate various metrics for each publisher:

COUNT(*) -- Counts number of books
SUM(b.stock_level) -- Adds up all books in stock
AVG(b.price) -- Calculates average price
COUNT(CASE WHEN b.stock_level = 0 THEN 1 END) -- Counts out-of-stock books

We group by publisher:

GROUP BY p.id, p.name

Finally, we order by the number of books:

ORDER BY book_count DESC