Add set operator challenges

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

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+---
+title: Expensive Books
+description: Practice creating a report with multiple tables
+order: 100
+type: challenge
+setup: |
+  ```sql
+  CREATE TABLE fiction_book (
+      id INT PRIMARY KEY,
+      title VARCHAR(255),
+      author VARCHAR(255),
+      price DECIMAL(10, 2)
+  );
+
+  CREATE TABLE non_fiction_book (
+      id INT PRIMARY KEY,
+      title VARCHAR(255),
+      author VARCHAR(255),
+      price DECIMAL(10, 2)
+  );
+
+  INSERT INTO fiction_book (id, title, author, price)
+  VALUES 
+      (1, 'The Great Gatsby', 'F. Scott Fitzgerald', 24.99),
+      (2, '1984', 'George Orwell', 19.99),
+      (3, 'Pride and Prejudice', 'Jane Austen', 15.99),
+      (4, 'The Hobbit', 'J.R.R. Tolkien', 29.99),
+      (5, 'The Doors of Perception', 'Aldous Huxley', 12.99);
+
+  INSERT INTO non_fiction_book (id, title, author, price)
+  VALUES 
+      (1, 'A Brief History of Time', 'Stephen Hawking', 29.99),
+      (2, 'The Art of War', 'Sun Tzu', 19.99),
+      (3, 'Sapiens', 'Yuval Noah Harari', 24.99),
+      (4, 'Pride and Prejudice: A Study Guide', 'John Smith', 12.99),
+      (5, 'The Doors of Perception', 'Aldous Huxley', 12.99);
+
+  CREATE TABLE summer_read (
+      id INT PRIMARY KEY,
+      title VARCHAR(255),
+      author VARCHAR(255),
+      price DECIMAL(10, 2)
+  );
+
+  INSERT INTO summer_read (id, title, author, price)
+  VALUES 
+      (1, 'The Great Gatsby', 'F. Scott Fitzgerald', 24.99),
+      (2, 'Sapiens', 'Yuval Noah Harari', 24.99),
+      (3, 'The Art of War', 'Sun Tzu', 19.99);
+  ```
+---
+
+Given the following three tables with the given data:
+
+> `fiction_book` table has the following data:
+
+| id  | title                   | author              | price |
+| --- | ----------------------- | ------------------- | ----- |
+| 1   | The Great Gatsby        | F. Scott Fitzgerald | 24.99 |
+| 2   | 1984                    | George Orwell       | 19.99 |
+| 3   | Pride and Prejudice     | Jane Austen         | 15.99 |
+| 4   | The Hobbit              | J.R.R. Tolkien      | 29.99 |
+| 5   | The Doors of Perception | Aldous Huxley       | 12.99 |
+
+> `non_fiction_book` table looks like this:
+
+| id  | title                              | author            | price |
+| --- | ---------------------------------- | ----------------- | ----- |
+| 1   | A Brief History of Time            | Stephen Hawking   | 29.99 |
+| 2   | The Art of War                     | Sun Tzu           | 19.99 |
+| 3   | Sapiens                            | Yuval Noah Harari | 24.99 |
+| 4   | Pride and Prejudice: A Study Guide | John Smith        | 12.99 |
+| 5   | The Doors of Perception            | Aldous Huxley     | 12.99 |
+
+> `summer_read` table has the following data:
+
+| id  | title            | author              | price |
+| --- | ---------------- | ------------------- | ----- |
+| 1   | The Great Gatsby | F. Scott Fitzgerald | 24.99 |
+| 2   | Sapiens          | Yuval Noah Harari   | 24.99 |
+| 3   | The Art of War   | Sun Tzu             | 19.99 |
+
+Write a query to find the books in all three tables that cost more than $20 along with their section i.e. `Fiction`, `Non-Fiction`, and `Summer Read`.
+
+> It's okay if the books are repeated in the result set. Important thing is to show the section and the book details.
+
+## Expected Results
+
+Your output should look like this:
+
+| id  | title                   | price | section     |
+| --- | ----------------------- | ----- | ----------- |
+| 4   | The Hobbit              | 29.99 | Fiction     |
+| 1   | The Great Gatsby        | 24.99 | Fiction     |
+| 1   | A Brief History of Time | 29.99 | Non-Fiction |
+| 1   | The Great Gatsby        | 24.99 | Summer Read |
+| 2   | Sapiens                 | 24.99 | Summer Read |
+| 3   | Sapiens                 | 24.99 | Non-Fiction |
+
+## Solution
+
+```sql
+SELECT id, title, price, 'Fiction' as section
+FROM fiction_book WHERE price > 20
+UNION
+SELECT id, title, price, 'Non-Fiction' as section
+FROM non_fiction_book WHERE price > 20
+UNION
+SELECT id, title, price, 'Summer Read' as section
+FROM summer_read WHERE price > 20
+```

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

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+---
+title: Multi-Section Authors
+description: Practice creating a report with multiple tables
+order: 100
+type: challenge
+setup: |
+  ```sql
+  CREATE TABLE fiction_book (
+      id INT PRIMARY KEY,
+      title VARCHAR(255),
+      author VARCHAR(255),
+      price DECIMAL(10, 2)
+  );
+
+  CREATE TABLE non_fiction_book (
+      id INT PRIMARY KEY,
+      title VARCHAR(255),
+      author VARCHAR(255),
+      price DECIMAL(10, 2)
+  );
+
+  INSERT INTO fiction_book (id, title, author, price)
+  VALUES 
+      (1, 'The Great Gatsby', 'F. Scott Fitzgerald', 24.99),
+      (2, '1984', 'George Orwell', 19.99),
+      (3, 'Pride and Prejudice', 'Jane Austen', 15.99),
+      (4, 'The Hobbit', 'J.R.R. Tolkien', 29.99),
+      (5, 'The Doors of Perception', 'Aldous Huxley', 12.99);
+
+  INSERT INTO non_fiction_book (id, title, author, price)
+  VALUES 
+      (1, 'A Brief History of Time', 'Stephen Hawking', 29.99),
+      (2, 'The Art of War', 'Sun Tzu', 19.99),
+      (3, 'Sapiens', 'Yuval Noah Harari', 24.99),
+      (4, 'Pride and Prejudice: A Study Guide', 'John Smith', 12.99),
+      (5, 'The Doors of Perception', 'Aldous Huxley', 12.99);
+  ```
+---
+
+Given the following two tables `fiction_book` and `non_fiction_book` with the following data:
+
+> `fiction_book` table has the following data
+
+| id  | title                   | author              | price |
+| --- | ----------------------- | ------------------- | ----- |
+| 1   | The Great Gatsby        | F. Scott Fitzgerald | 24.99 |
+| 2   | 1984                    | George Orwell       | 19.99 |
+| 3   | Pride and Prejudice     | Jane Austen         | 15.99 |
+| 4   | The Hobbit              | J.R.R. Tolkien      | 29.99 |
+| 5   | The Doors of Perception | Aldous Huxley       | 12.99 |
+
+> `non_fiction_book` table looks like this:
+
+| id  | title                              | author            | price |
+| --- | ---------------------------------- | ----------------- | ----- |
+| 1   | A Brief History of Time            | Stephen Hawking   | 29.99 |
+| 2   | The Art of War                     | Sun Tzu           | 19.99 |
+| 3   | Sapiens                            | Yuval Noah Harari | 24.99 |
+| 4   | Pride and Prejudice: A Study Guide | John Smith        | 12.99 |
+| 5   | The Doors of Perception            | Aldous Huxley     | 12.99 |
+
+Write a query to find the authors who have written books in both `fiction_book` and `non_fiction_book` tables. 
+
+## Expected Results
+
+Your output should only contain the author names:
+
+| author              |
+| ------------------- |
+| Aldous Huxley       |
+
+## Solution
+
+```sql
+SELECT author
+FROM fiction_book
+INTERSECT
+SELECT author
+FROM non_fiction_book;
+```