Add new challenges

src/data/courses/sql-mastery/chapters/multi-table-queries/lessons/expensive-books.md

@@ -1,7 +1,7 @@
 ---
 title: Expensive Books
 description: Practice creating a report with multiple tables
-order: 110
+order: 190
 type: challenge
 setup: |
   ```sql

src/data/courses/sql-mastery/chapters/multi-table-queries/lessons/high-value-orders.md

@@ -1,7 +1,7 @@
 ---
 title: High Value Orders
 description: Practice using EXCEPT to identify potential technical book opportunities
-order: 110
+order: 130
 type: challenge
 setup: |
   ```sql
@@ -39,9 +39,7 @@ setup: |
   ```
 ---
 
-The bookstore wants to identify the highest value orders i.e. the orders worth more than or equal to $500. Write a query to find order amounts, dates along with the customer names.
-
-We have the `customer` and `sale` tables.
+Given the following three tables you are required to write a query to find the orders worth more than or equal to $500.
 
 > `customer` table has the list of customers.
 
@@ -66,13 +64,13 @@ We have the `customer` and `sale` tables.
 | 6   | 2           | 2024-11-23 | 300.00       |
 | 7   | 2           | 2024-11-11 | 300.00       |
 
-Write a query to find the orders above $500 along with the information of the customers. Your output should have the following columns:
+Your output should contain the orders with amount greater than or equal to `$500` and the following columns for each order:
 
 - `customer_name`
 - `order_amount`
 - `order_date`
 
-The output should be ordered by the `order_amount` in descending order.
+Results should be sorted by `order_amount` in descending order.
 
 ## Expected Output
 

src/data/courses/sql-mastery/chapters/multi-table-queries/lessons/inactive-customers.md

@@ -39,7 +39,7 @@ setup: |
   ```
 ---
 
-Our bookstore has some marketing budget. The marketing team wants to send coupons to customers who have never placed an order. They have asked us to extract the list of customers for them.
+Given the following data in `customer` and `sale` tables, we need to find the customers who have never placed an order.
 
 We have the `customer` and `sale` tables.
 

src/data/courses/sql-mastery/chapters/multi-table-queries/lessons/multi-section-authors.md

@@ -1,7 +1,7 @@
 ---
 title: Multi-Section Authors
 description: Practice creating a report with multiple tables
-order: 120
+order: 180
 type: challenge
 setup: |
   ```sql

src/data/courses/sql-mastery/chapters/multi-table-queries/lessons/recent-orders.md

@@ -39,9 +39,7 @@ setup: |
   ```
 ---
 
-The bookstore wants to display the 3 most recent orders placed by customers. Write a query to retrieve the customer names, order dates, and total amounts of these orders, ordered by the most recent first.
-
-We have the `customer` and `sale` tables.
+Given the following data in `customer` and `sale` tables, we want to track the recent orders in our bookstore.
 
 > `customer` table has the list of customers.
 
@@ -66,7 +64,7 @@ We have the `customer` and `sale` tables.
 | 6   | 2           | 2024-11-23 | 300.00       |
 | 7   | 2           | 2024-11-11 | 300.00       |
 
-Write a query to find the 3 most recent orders along with the information of the customers. Your output should have the following columns:
+Write a query to find the 3 most recent orders along with customer information. Your output should have the following columns:
 
 - `customer_name`
 - `order_date`

src/data/courses/sql-mastery/chapters/multi-table-queries/lessons/referred-customers.md

@@ -0,0 +1,66 @@
+---
+title: Referred Customers
+description: Practice using joins to find customers who have been referred by another customer
+order: 150
+type: challenge
+setup: |
+  ```sql
+  CREATE TABLE customer (
+      id INT PRIMARY KEY,
+      name VARCHAR(255),
+      email VARCHAR(255),
+      referred_by INT
+  );
+
+  INSERT INTO customer (id, name, email, referred_by)
+  VALUES 
+      (1, 'Alice Smith', 'alice@example.com', NULL),
+      (2, 'Bob Johnson', 'bob@example.com', 1),
+      (3, 'Carol White', 'carol@example.com', 1),
+      (4, 'David Brown', 'david@example.com', 2),
+      (5, 'Emily Davis', 'emily@example.com', NULL);
+  ```
+---
+
+The bookstore runs a referral program where existing customers can refer new customers. Each referred customer records the ID of the referring customer in the database.
+
+Write a query to find the names and email addresses of customers who have referred at least one other customer.
+
+You can use the data from the existing `customer` table.
+
+| customer_id | name        | email             | referred_by |
+| ----------- | ----------- | ----------------- | ----------- |
+| 1           | Alice Smith | alice@example.com | NULL        |
+| 2           | Bob Johnson | bob@example.com   | 1           |
+| 3           | Carol White | carol@example.com | 1           |
+| 4           | David Brown | david@example.com | 2           |
+| 5           | Emily Davis | emily@example.com | NULL        |
+
+Your output should contain the following columns:
+
+- `name`
+- `email`
+- `referred_by` (name of the customer or '- None -')
+
+> **Tip:** You can use `COALESCE` function for `referred_by` column.
+
+## Expected Output
+
+| name        | email             | referred_by |
+| ----------- | ----------------- | ----------- |
+| Carol White | carol@example.com | Alice Smith |
+| Bob Johnson | bob@example.com   | Alice Smith |
+| David Brown | david@example.com | Bob Johnson |
+| Emily Davis | emily@example.com | - None -    |
+| Alice Smith | alice@example.com | - None -    |
+
+## Solution
+
+```sql
+SELECT
+    c.name,
+    c.email,
+    COALESCE(r.name, '- None -') AS referred_by
+FROM customer c
+LEFT JOIN customer r ON c.referred_by = r.id;
+```

src/data/courses/sql-mastery/chapters/multi-table-queries/lessons/specific-book-customers.md

@@ -0,0 +1,118 @@
+---
+title: Specific Book Customers
+description: Practice using joins to find customers who have bought a specific book
+order: 140
+type: challenge
+setup: |
+  ```sql
+  CREATE TABLE customer (
+      id INT PRIMARY KEY,
+      name VARCHAR(255),
+      email VARCHAR(255)
+  );
+
+  CREATE TABLE sale (
+      id INT PRIMARY KEY,
+      customer_id INT,
+      book_id INT,
+      order_date DATE,
+      total_amount DECIMAL(10,2)
+  );
+
+  CREATE TABLE book (
+      id INT PRIMARY KEY,
+      title VARCHAR(255),
+      author VARCHAR(255)
+  );
+
+  INSERT INTO book (id, title, author)
+  VALUES 
+      (1, 'The Great Gatsby', 'F. Scott Fitzgerald'),
+      (2, 'To Kill a Mockingbird', 'Harper Lee'),
+      (3, '1984', 'George Orwell'),
+      (4, 'Pride and Prejudice', 'Jane Austen'),
+      (5, 'The Catcher in the Rye', 'J.D. Salinger');
+
+  INSERT INTO customer (id, name, email)
+  VALUES 
+      (1, 'John Doe', 'john.doe@example.com'),
+      (2, 'Jane Smith', 'jane.smith@example.com'),
+      (3, 'Alice Johnson', 'alice.johnson@example.com'),
+      (4, 'Bob Brown', 'bob.brown@example.com'),
+      (5, 'Charlie Davis', 'charlie.davis@example.com'),
+      (6, 'David Lee', 'david.lee@example.com');
+
+  INSERT INTO sale (id, customer_id, book_id, order_date, total_amount)
+  VALUES 
+      (1, 1, 1, '2024-12-02', 100.00),
+      (2, 1, 2, '2024-11-15', 150.00),
+      (3, 1, 3, '2024-10-20', 200.00),
+      (4, 4, 4, '2024-12-26', 250.00),
+      (5, 5, 5, '2024-11-12', 300.00),
+      (6, 2, 1, '2024-11-23', 300.00),
+      (7, 2, 2, '2024-11-11', 300.00);
+  ```
+---
+
+We have following three tables `customer`, `sale`, and `book`. You are required to write a query to find all customers who have purchased any book by "Harper Lee".
+
+> `customer` table has the list of customers.
+
+| id  | name          | email                     |
+| --- | ------------- | ------------------------- |
+| 1   | John Doe      | john.doe@example.com      |
+| 2   | Jane Smith    | jane.smith@example.com    |
+| 3   | Alice Johnson | alice.johnson@example.com |
+| 4   | Bob Brown     | bob.brown@example.com     |
+| 5   | Charlie Davis | charlie.davis@example.com |
+| 6   | David Lee     | david.lee@example.com     |
+
+> `sale` table has the list of sales made to customers.
+
+| id  | customer_id | order_date | total_amount |
+| --- | ----------- | ---------- | ------------ |
+| 1   | 1           | 2024-12-02 | 100.00       |
+| 2   | 1           | 2024-11-15 | 150.00       |
+| 3   | 1           | 2024-10-20 | 200.00       |
+| 4   | 4           | 2024-12-26 | 250.00       |
+| 5   | 5           | 2024-11-12 | 300.00       |
+| 6   | 2           | 2024-11-23 | 300.00       |
+| 7   | 2           | 2024-11-11 | 300.00       |
+
+> `book` table has the list of books.
+
+| id  | title                  | author              |
+| --- | ---------------------- | ------------------- |
+| 1   | The Great Gatsby       | F. Scott Fitzgerald |
+| 2   | To Kill a Mockingbird  | Harper Lee          |
+| 3   | 1984                   | George Orwell       |
+| 4   | Pride and Prejudice    | Jane Austen         |
+| 5   | The Catcher in the Rye | J.D. Salinger       |
+
+## Expected Output
+
+The expected output should be a list of customers who have purchased any book by "Harper Lee" with their id, name, title of the book they purchased and the date of the purchase.
+
+| id  | name       | title                 | purchase_date     |
+| --- | ---------- | --------------------- | ----------------- |
+| 1   | John Doe   | To Kill a Mockingbird | November 15, 2024 |
+| 2   | Jane Smith | To Kill a Mockingbird | November 11, 2024 |
+
+## Solution
+
+```sql
+SELECT
+    c.id,
+    c.name,
+    c.email,
+    b.title,
+    TO_CHAR(s.order_date, 'Month, DD, YYYY') purchase_date
+FROM
+    customer c
+INNER JOIN
+    sale s on c.id = s.customer_id
+INNER JOIN
+    book b ON s.book_id = b.id
+WHERE
+    b.author = 'Harper Lee'
+```

src/data/courses/sql-mastery/chapters/multi-table-queries/lessons/trending-tech-books.md

@@ -1,7 +1,7 @@
 ---
 title: Trending Tech Books
 description: Practice using EXCEPT to identify potential technical book opportunities
-order: 100
+order: 200
 type: challenge
 setup: |
   ```sql
@@ -59,7 +59,7 @@ You have access to two tables: `trending_book` which tracks currently popular bo
 | 4   | Python Crash Course        | Python               | 34.99 |
 | 5   | Head First Java            | Java                 | 44.99 |
 
-Write a query to find the technical books that are not currently trending. This will help the publisher to review the books that are not currently popular and consider creating new editions or improving the existing ones.
+Write a query to find the technical books that are not currently trending. **Hint:** you can use one of the set operations.
 
 ## Expected Results