Add new challenges

src/data/courses/sql-mastery/chapters/scalar-functions/lessons/book-performance.md

@@ -0,0 +1,86 @@
+---
+title: Book Performance
+description: Practice using CASE expressions and GROUP BY for book analysis
+order: 220
+type: challenge
+setup: |
+  ```sql
+  CREATE TABLE book (
+      id INT PRIMARY KEY,
+      title VARCHAR(100),
+      category VARCHAR(50),
+      rating DECIMAL(3,1),
+      published_year INT,
+      total_reviews INT
+  );
+
+  INSERT INTO book (id, title, category, rating, published_year, total_reviews) VALUES
+      (1, 'SQL Basics', 'Programming', 4.5, 2020, 120),
+      (2, 'Advanced Queries', 'Programming', 4.8, 2021, 85),
+      (3, 'Database Design', 'Database', 4.2, 2019, 150),
+      (4, 'Query Optimization', 'Database', 4.6, 2022, 65),
+      (5, 'Data Modeling', 'Database', 2.9, 2021, 45),
+      (6, 'PostgreSQL Tips', 'Programming', 4.7, 2023, 95),
+      (7, 'NoSQL Concepts', 'Database', 4.3, 2022, 75),
+      (8, 'SQL for Beginners', 'Programming', 4.4, 2020, 200);
+  ```
+---
+
+The book store wants to analyze their book sales. They need a report that shows book performance by category and rating.
+
+Given the following data in table `book`:
+
+| id  | title              | category    | rating | total_reviews |
+| --- | ------------------ | ----------- | ------ | ------------- |
+| 1   | SQL Basics         | Programming | 4.5    | 120           |
+| 2   | Advanced Queries   | Programming | 4.8    | 85            |
+| 3   | Database Design    | Database    | 4.2    | 150           |
+| 4   | Query Optimization | Database    | 4.6    | 65            |
+| 5   | Data Modeling      | Database    | 2.9    | 45            |
+| 6   | PostgreSQL Tips    | Programming | 4.7    | 95            |
+| 7   | NoSQL Concepts     | Database    | 4.3    | 75            |
+| 8   | SQL for Beginners  | Programming | 4.4    | 200           |
+
+Write a query that shows:
+
+- Category
+- Rating group:
+  - `Outstanding` if rating >= 4.5
+  - `Good` if rating >= 4.0
+  - `Average` if rating >= 3.5
+  - `Poor` if rating >= 3.0
+- Number of books in each group
+
+## Expected Output
+
+| category    | rating_group | book_count |
+| ----------- | ------------ | ---------- |
+| Database    | Poor         | 1          |
+| Database    | Outstanding  | 1          |
+| Database    | Good         | 2          |
+| Programming | Outstanding  | 3          |
+| Programming | Good         | 1          |
+
+## Solution
+
+```sql
+SELECT
+    category,
+    CASE
+        WHEN rating >= 4.5 THEN 'Outstanding'
+        WHEN rating >= 4.0 THEN 'Good'
+        WHEN rating >= 3.5 THEN 'Average'
+        ELSE 'Poor'
+    END as rating_group,
+    COUNT(*) as book_count
+FROM book
+GROUP BY
+    category,
+    CASE
+        WHEN rating >= 4.5 THEN 'Outstanding'
+        WHEN rating >= 4.0 THEN 'Good'
+        WHEN rating >= 3.5 THEN 'Average'
+        ELSE 'Poor'
+    END
+ORDER BY category, rating_group DESC;
+```

src/data/courses/sql-mastery/chapters/scalar-functions/lessons/book-sale-categories.md

@@ -24,18 +24,18 @@ setup: |
   ```
 ---
 
-A library needs to analyze their SQL book collection. They want a report that categorizes books based on various criteria.
+The bookstore manager wants to analyze the SQL book collection. They want a report that categorizes books based on various criteria.
 
 Given the following data in table `book`:
 
-| id  | title              | page_count | publish_year | copies_in_stock | monthly_rentals |
-| --- | ------------------ | ---------- | ------------ | --------------- | --------------- |
-| 1   | SQL Basics         | 250        | 2020         | 5               | 12              |
-| 2   | Advanced Queries   | 450        | 2021         | 3               | 8               |
-| 3   | Database Design    | 350        | 2019         | 10              | 15              |
-| 4   | Query Optimization | 275        | 2022         | 2               | 6               |
-| 5   | Data Modeling      | 400        | 2021         | 1               | 4               |
-| 6   | PostgreSQL Tips    | 200        | 2023         | 8               | 20              |
+| title              | page_count | copies_in_stock | monthly_rentals |
+| ------------------ | ---------- | --------------- | --------------- |
+| SQL Basics         | 250        | 5               | 12              |
+| Advanced Queries   | 450        | 3               | 8               |
+| Database Design    | 350        | 10              | 15              |
+| Query Optimization | 275        | 2               | 6               |
+| Data Modeling      | 400        | 1               | 4               |
+| PostgreSQL Tips    | 200        | 8               | 20              |
 
 Write a query that shows:
 
@@ -44,10 +44,6 @@ Write a query that shows:
   - `Short` if page_count < 300
   - `Medium` if page_count between 300 and 400
   - `Long` if page_count > 400
-- Publication status:
-  - `Recent` if publish_year >= 2022
-  - `Current` if publish_year is 2020 or 2021
-  - `Older` if publish_year < 2020
 - Stock status:
   - `Low` if copies_in_stock < 3
   - `Medium` if copies_in_stock between 3 and 7
@@ -59,15 +55,14 @@ Write a query that shows:
 
 ## Expected Output
 
-| title              | length_category | publication_status | stock_status | popularity    |
-| ------------------ | --------------- | ------------------ | ------------ | ------------- |
-| PostgreSQL Tips    | Short           | Recent             | High         | High Demand   |
-| Database Design    | Medium          | Older              | High         | High Demand   |
-| SQL Basics         | Short           | Current            | Medium       | Medium Demand |
-| Advanced Queries   | Long            | Current            | Medium       | Medium Demand |
-| Query Optimization | Short           | Recent             | Low          | Medium Demand |
-
-Data Modeling Medium Current Low Low Demand
+| title              | length_category | stock_status | popularity    |
+| ------------------ | --------------- | ------------ | ------------- |
+| PostgreSQL Tips    | Short           | High         | High Demand   |
+| Database Design    | Medium          | High         | High Demand   |
+| SQL Basics         | Short           | Medium       | Medium Demand |
+| Advanced Queries   | Long            | Medium       | Medium Demand |
+| Query Optimization | Short           | Low          | Medium Demand |
+| Data Modeling      | Medium          | Low          | Low Demand    |
 
 ## Solution
 
@@ -79,11 +74,6 @@ SELECT
         WHEN page_count <= 400 THEN 'Medium'
         ELSE 'Long'
     END as length_category,
-    CASE
-        WHEN publish_year >= 2022 THEN 'Recent'
-        WHEN publish_year >= 2020 THEN 'Current'
-        ELSE 'Older'
-    END as publication_status,
     CASE
         WHEN copies_in_stock < 3 THEN 'Low'
         WHEN copies_in_stock <= 7 THEN 'Medium'
@@ -94,6 +84,6 @@ SELECT
         WHEN monthly_rentals >= 6 THEN 'Medium Demand'
         ELSE 'Low Demand'
     END as popularity
-FROM books
+FROM book
 ORDER BY monthly_rentals DESC;
 ```