Why grouping is needed in SQL - See It in Action

Understanding Why Grouping is Needed in SQL

📖 Scenario: You work at a small bookstore. You have a list of sales records showing which book was sold and how many copies. You want to find out how many copies of each book were sold in total.

🎯 Goal: Build a SQL query that groups sales by book title and calculates the total copies sold for each book.

📋 What You'll Learn

Create a table called sales with columns book_title and copies_sold

Insert the exact sales data provided

Write a SQL query that groups the sales by book_title

Use SUM() to calculate total copies sold per book

💡 Why This Matters

🌍 Real World

Grouping data is common in sales reports, inventory summaries, and any situation where you want totals or averages per category.

💼 Career

Understanding GROUP BY is essential for data analysis, reporting, and writing effective SQL queries in many jobs.

1

Create the sales table and insert data

Create a table called sales with columns book_title (text) and copies_sold (integer). Insert these exact rows: ('The Hobbit', 3), ('1984', 5), ('The Hobbit', 2), ('Dune', 4), ('1984', 1).

SQL

-- Create table sales and insert data
-- Your code here

Need a hint?

Use CREATE TABLE to make the table and INSERT INTO to add the rows.

2

Add a query to group sales by book

Write a SQL query that selects book_title and the total copies sold for each book. Use GROUP BY book_title to group the rows by book title.

SQL

CREATE TABLE sales (book_title TEXT, copies_sold INTEGER);
INSERT INTO sales (book_title, copies_sold) VALUES
('The Hobbit', 3),
('1984', 5),
('The Hobbit', 2),
('Dune', 4),
('1984', 1);

-- Write a query to group sales by book_title
-- Your code here

Need a hint?

Use SUM(copies_sold) to add copies sold per book and GROUP BY book_title to group rows.

3

Explain why grouping is needed

Add a comment explaining why GROUP BY is needed in this query to get total copies sold per book.

SQL

CREATE TABLE sales (book_title TEXT, copies_sold INTEGER);
INSERT INTO sales (book_title, copies_sold) VALUES
('The Hobbit', 3),
('1984', 5),
('The Hobbit', 2),
('Dune', 4),
('1984', 1);

SELECT book_title, SUM(copies_sold) AS total_copies
FROM sales
GROUP BY book_title;

-- Add a comment explaining why GROUP BY is needed
-- Your code here

Need a hint?

Think about how grouping helps add up sales for each book instead of all sales together.

4

Complete the query with ordering

Add ORDER BY total_copies DESC to the query to show books with the highest total copies sold first.

SQL

CREATE TABLE sales (book_title TEXT, copies_sold INTEGER);
INSERT INTO sales (book_title, copies_sold) VALUES
('The Hobbit', 3),
('1984', 5),
('The Hobbit', 2),
('Dune', 4),
('1984', 1);

SELECT book_title, SUM(copies_sold) AS total_copies
FROM sales
GROUP BY book_title
-- Add ORDER BY to sort by total_copies descending
-- Your code here

Need a hint?

Use ORDER BY total_copies DESC to sort results from highest to lowest total copies sold.