Add subquery challenge

2 weeks ago · 7ba9463949
parent 3da4035851
commit 7ba9463949
1 changed files with 89 additions and 0 deletions
--- a/src/data/courses/sql-mastery/chapters/subqueries-and-ctes/lessons/above-average-books.md
+++ b/src/data/courses/sql-mastery/chapters/subqueries-and-ctes/lessons/above-average-books.md
@ -0,0 +1,89 @@
+---
+title: Above Average Books
+description: Practice using scalar subqueries to find books above average price in their category
+order: 140
+type: challenge
+setup: |
+  ```sql
+  CREATE TABLE book (
+      id INT PRIMARY KEY,
+      title VARCHAR(100),
+      category VARCHAR(50),
+      price DECIMAL(10,2),
+      published_date DATE
+  );
+
+  INSERT INTO book (id, title, category, price, published_date) VALUES
+      (1, 'SQL Basics', 'Programming', 29.99, '2024-01-15'),
+      (2, 'Advanced SQL', 'Programming', 49.99, '2024-02-20'),
+      (3, 'Data Science', 'Data Analysis', 39.99, '2024-01-10'),
+      (4, 'Web Development', 'Programming', 34.99, '2024-03-01'),
+      (5, 'Statistics 101', 'Data Analysis', 24.99, '2024-02-15'),
+      (6, 'Machine Learning', 'Data Analysis', 44.99, '2024-03-15'),
+      (7, 'Database Design', 'Programming', 39.99, '2024-01-20'),
+      (8, 'Python Basics', 'Programming', 29.99, '2024-02-01');
+  ```
+---
+
+The bookstore manager wants to identify books that are priced above the average price in their respective categories, but only for books published in 2024. This information will help in adjusting pricing strategies.
+
+Given the following data in table `book`:
+
+| id  | title            | category      | price | published_date |
+| --- | ---------------- | ------------- | ----- | -------------- |
+| 1   | SQL Basics       | Programming   | 29.99 | 2024-01-15     |
+| 2   | Advanced SQL     | Programming   | 49.99 | 2024-02-20     |
+| 3   | Data Science     | Data Analysis | 39.99 | 2024-01-10     |
+| 4   | Web Development  | Programming   | 34.99 | 2024-03-01     |
+| 5   | Statistics 101   | Data Analysis | 24.99 | 2024-02-15     |
+| 6   | Machine Learning | Data Analysis | 44.99 | 2024-03-15     |
+| 7   | Database Design  | Programming   | 39.99 | 2024-01-20     |
+| 8   | Python Basics    | Programming   | 29.99 | 2024-02-01     |
+
+Write a query that shows:
+
+- Book title
+- Category
+- Book price
+- Category average price (rounded to 2 decimal places)
+- Price difference from category average (rounded to 2 decimal places)
+
+Only include books that are:
+
+1. Published in 2024
+2. Priced above their category's average price
+
+## Expected Output
+
+| title            | category      | price | category_avg | price_diff |
+| ---------------- | ------------- | ----- | ------------ | ---------- |
+| Machine Learning | Data Analysis | 44.99 | 36.66        | 8.33       |
+| Data Science     | Data Analysis | 39.99 | 36.66        | 3.33       |
+| Advanced SQL     | Programming   | 49.99 | 36.99        | 13.00      |
+| Database Design  | Programming   | 39.99 | 36.99        | 3.00       |
+
+## Solution
+
+```sql
+SELECT
+    b1.title,
+    b1.category,
+    b1.price,
+    ROUND(avg_price, 2) AS category_avg,
+    ROUND(b1.price - avg_price, 2) AS price_diff
+FROM book b1
+INNER JOIN (
+    -- Subquery to calculate average price per category for 2024
+    SELECT
+        category,
+        AVG(price) AS avg_price
+    FROM book
+    WHERE EXTRACT(YEAR FROM published_date) = 2024
+    GROUP BY category
+) AS ca ON b1.category = ca.category
+WHERE
+    EXTRACT(YEAR FROM b1.published_date) = 2024 -- Filter for books published in 2024
+    AND b1.price > ca.avg_price                 -- Filter books above category average
+ORDER BY
+    b1.category, price_diff DESC;               -- Sort results
+```