GROUP BY with ORDER BY in SQL - Mini Project: Build & Apply

GROUP BY with ORDER BY in SQL

📖 Scenario: You work for a small bookstore. The store keeps a record of every sale in a table called sales. Each sale has the book's title, the author, and the quantity sold.The manager wants to see how many copies of each book have been sold in total, sorted from the most sold to the least sold.

🎯 Goal: Create an SQL query that groups the sales by title and author, sums the total quantity sold for each book, and orders the results by the total quantity sold in descending order.

📋 What You'll Learn

Use the sales table with columns title, author, and quantity

Group the results by title and author

Calculate the total quantity sold for each book using SUM(quantity)

Order the results by the total quantity sold in descending order

💡 Why This Matters

🌍 Real World

Bookstores and many businesses use GROUP BY with ORDER BY to summarize and rank sales data.

💼 Career

Understanding how to group and order data is essential for data analysis and reporting roles.

1

Create the sales table with sample data

Write an SQL statement to create a table called sales with columns title (text), author (text), and quantity (integer). Then insert these exact rows: ('The Hobbit', 'J.R.R. Tolkien', 5), ('The Hobbit', 'J.R.R. Tolkien', 3), ('1984', 'George Orwell', 4), ('1984', 'George Orwell', 2), ('Dune', 'Frank Herbert', 6).

SQL

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

Hint

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

2

Add a variable for the total quantity alias

Write an SQL query that selects title, author, and the sum of quantity as total_quantity from the sales table. Use SUM(quantity) AS total_quantity in the SELECT clause.

SQL

CREATE TABLE sales (
  title TEXT,
  author TEXT,
  quantity INTEGER
);

INSERT INTO sales (title, author, quantity) VALUES
('The Hobbit', 'J.R.R. Tolkien', 5),
('The Hobbit', 'J.R.R. Tolkien', 3),
('1984', 'George Orwell', 4),
('1984', 'George Orwell', 2),
('Dune', 'Frank Herbert', 6);

-- Select title, author, and sum of quantity as total_quantity
SELECT title, author, SUM(quantity) AS total_quantity
FROM sales
-- Your code here

Hint

Use SUM(quantity) AS total_quantity to calculate the total copies sold per book.

3

Group the sales by title and author

Add a GROUP BY clause to the query to group the results by title and author.

SQL

CREATE TABLE sales (
  title TEXT,
  author TEXT,
  quantity INTEGER
);

INSERT INTO sales (title, author, quantity) VALUES
('The Hobbit', 'J.R.R. Tolkien', 5),
('The Hobbit', 'J.R.R. Tolkien', 3),
('1984', 'George Orwell', 4),
('1984', 'George Orwell', 2),
('Dune', 'Frank Herbert', 6);

SELECT title, author, SUM(quantity) AS total_quantity
FROM sales
GROUP BY title, author
-- Your code here

Hint

Use GROUP BY title, author to group the sales by book.

4

Order the results by total quantity sold descending

Add an ORDER BY clause to the query to sort the results by total_quantity in descending order.

SQL

CREATE TABLE sales (
  title TEXT,
  author TEXT,
  quantity INTEGER
);

INSERT INTO sales (title, author, quantity) VALUES
('The Hobbit', 'J.R.R. Tolkien', 5),
('The Hobbit', 'J.R.R. Tolkien', 3),
('1984', 'George Orwell', 4),
('1984', 'George Orwell', 2),
('Dune', 'Frank Herbert', 6);

SELECT title, author, SUM(quantity) AS total_quantity
FROM sales
GROUP BY title, author
ORDER BY total_quantity DESC
-- Your code here

Hint

Use ORDER BY total_quantity DESC to sort from highest to lowest total sold.

Practice

1. What does the GROUP BY clause do in an SQL query?

easy

A. It deletes duplicate rows from the table.

B. It sorts the rows in ascending order.

C. It groups rows that have the same values in specified columns.

D. It limits the number of rows returned.

Solution

1. Step 1: Understand the purpose of GROUP BY

   The GROUP BY clause collects rows with the same values in specified columns into summary rows.

2. Step 2: Differentiate from other clauses

   ORDER BY sorts rows, DELETE removes rows, and LIMIT restricts output count, which are different from grouping.

3. Final Answer:

   It groups rows that have the same values in specified columns. -> Option C

4. Quick Check:

   GROUP BY = grouping rows [OK]

Hint: GROUP BY groups rows by column values, not sorting [OK]

Common Mistakes:

• Confusing GROUP BY with ORDER BY
• Thinking GROUP BY deletes duplicates
• Assuming GROUP BY limits rows

2. Which of the following SQL queries correctly groups sales by product and orders the result by total sales descending?

easy

A. SELECT product, SUM(amount) FROM sales GROUP BY product ORDER BY SUM(amount) DESC;

B. SELECT product, SUM(amount) FROM sales ORDER BY product GROUP BY SUM(amount) DESC;

C. SELECT product, SUM(amount) FROM sales GROUP BY product ORDER BY product DESC;

D. SELECT product, SUM(amount) FROM sales ORDER BY SUM(amount) GROUP BY product DESC;

Solution

1. Step 1: Check GROUP BY and ORDER BY order

   The correct syntax is GROUP BY first, then ORDER BY to sort grouped results.

2. Step 2: Verify ordering by aggregated column

   Ordering by SUM(amount) DESC sorts by total sales descending, matching the requirement.

3. Final Answer:

   SELECT product, SUM(amount) FROM sales GROUP BY product ORDER BY SUM(amount) DESC; -> Option A

4. Quick Check:

   GROUP BY then ORDER BY with aggregate [OK]

Hint: GROUP BY before ORDER BY; order by aggregate for totals [OK]

Common Mistakes:

• Swapping GROUP BY and ORDER BY order
• Ordering by non-aggregated columns incorrectly
• Using ORDER BY before GROUP BY

3. Given the table orders with columns customer_id and order_total, what will this query return?

SELECT customer_id, COUNT(*) AS order_count FROM orders GROUP BY customer_id ORDER BY order_count ASC;

medium

A. Syntax error due to incorrect ORDER BY usage.

B. List of customers with their order counts sorted from highest to lowest.

C. List of customers with total order amounts sorted ascending.

D. List of customers with their order counts sorted from lowest to highest.

Solution

1. Step 1: Understand the GROUP BY and COUNT

   The query groups rows by customer_id and counts orders per customer.

2. Step 2: Analyze ORDER BY order_count ASC

   Ordering by order_count ascending sorts customers from fewest to most orders.

3. Final Answer:

   List of customers with their order counts sorted from lowest to highest. -> Option D

4. Quick Check:

   ORDER BY ASC sorts ascending [OK]

Hint: ORDER BY ASC sorts from smallest to largest [OK]

Common Mistakes:

• Assuming ORDER BY ASC sorts descending
• Confusing COUNT with SUM
• Thinking query returns total order amounts

4. Identify the error in this SQL query:

SELECT department, COUNT(*) FROM employees ORDER BY COUNT(*) DESC GROUP BY department;

medium

A. GROUP BY must come before ORDER BY in the query.

B. COUNT(*) cannot be used in ORDER BY clause.

C. Missing alias for COUNT(*) causes syntax error.

D. ORDER BY cannot sort aggregated columns.

Solution

1. Step 1: Check SQL clause order

   GROUP BY must appear before ORDER BY in SQL syntax.

2. Step 2: Identify the error in clause sequence

   The query places ORDER BY before GROUP BY, causing syntax error.

3. Final Answer:

   GROUP BY must come before ORDER BY in the query. -> Option A

4. Quick Check:

   GROUP BY before ORDER BY [OK]

Hint: GROUP BY always before ORDER BY in SQL [OK]

Common Mistakes:

• Placing ORDER BY before GROUP BY
• Assuming COUNT(*) can't be in ORDER BY
• Forgetting clause order rules

5. You have a sales table with columns region, salesperson, and amount. You want to find the total sales per region, but only show regions with total sales above 1000, sorted by total sales descending. Which query achieves this?

hard

A. SELECT region, SUM(amount) FROM sales WHERE SUM(amount) > 1000 GROUP BY region ORDER BY SUM(amount) DESC;

B. SELECT region, SUM(amount) FROM sales GROUP BY region HAVING SUM(amount) > 1000 ORDER BY SUM(amount) DESC;

C. SELECT region, SUM(amount) FROM sales GROUP BY region ORDER BY SUM(amount) DESC HAVING SUM(amount) > 1000;

D. SELECT region, SUM(amount) FROM sales ORDER BY SUM(amount) DESC HAVING SUM(amount) > 1000 GROUP BY region;

Solution

1. Step 1: Use GROUP BY to group sales by region

   Grouping by region allows aggregation of sales per region.

2. Step 2: Filter groups with HAVING clause

   HAVING filters groups after aggregation; WHERE cannot filter on aggregates.

3. Step 3: Sort results with ORDER BY descending

   ORDER BY SUM(amount) DESC sorts regions by total sales from highest to lowest.

4. Final Answer:

   SELECT region, SUM(amount) FROM sales GROUP BY region HAVING SUM(amount) > 1000 ORDER BY SUM(amount) DESC; -> Option B

5. Quick Check:

   GROUP BY + HAVING + ORDER BY correct order [OK]

Hint: Use HAVING to filter grouped results, ORDER BY last [OK]

Common Mistakes:

• Using WHERE to filter aggregated results
• Placing HAVING after ORDER BY
• Incorrect clause order