Books and Authors

Problem

Table: Books

+---------------+---------+
| Column Name   | Type    |
+---------------+---------+
| book_id       | int     |
| title         | varchar |
| genre         | varchar |
+---------------+---------+
book_id is the primary key for this table.
This table contains information about the books in a library.

Table: Authors

+---------------+---------+
| Column Name   | Type    |
+---------------+---------+
| author_id     | int     |
| book_id       | int     |
| author_name   | varchar |
+---------------+---------+
(author_id, book_id) is the primary key for this table.
This table contains information about the authors of the books in the library.

Problem Definition

Write a solution to find the number of books each author has written in the genre 'Fiction'.

Return the result table with author_name and the number of books in 'Fiction' genre as fiction_books_count. If an author has not written any books in the 'Fiction' genre, they should not appear in the output.

Return the result table ordered by fiction_books_count in descending order. In case of a tie, order by author_name in ascending order.

Example

Input: 
Books table:
+---------+----------------------+---------------+
| book_id | title                | genre         |
+---------+---------------=------+---------------+
| 1       | War and Peace        | Fiction       |
| 2       | Anna Karenina        | Fiction       |
| 3       | Crime and Punishment | Fiction       |
| 4       | The Great Gatsby     | Fiction       |
| 5       | Pride and Prejudice  | Romance       |
+---------+----------------------+---------------+

Authors table:
+-----------+---------+---------------------+
| author_id | book_id | author_name         |
+-----------+---------+---------------------+
| 101       | 1       | Leo Tolstoy         |
| 101       | 2       | Leo Tolstoy         |
| 102       | 3       | Fyodor Dostoevsky   |
| 103       | 4       | F. Scott Fitzgerald |
| 104       | 5       | Jane Austen         |
+-----------+---------+---------------------+

Output: 
+---------------------+---------------------+
| author_name         | fiction_books_count |
+---------------------+---------------------+
| Leo Tolstoy         | 2                   |
| F. Scott Fitzgerald | 1                   |
| Fyodor Dostoevsky   | 1                   |
+---------------------+---------------------+

Try It Yourself

-- TODO: Write your user queries here

Solution

To identify the number of books each author has written in the 'Fiction' genre, we can employ SQL's JOIN, GROUP BY, and aggregation functions. The solution involves joining the Authors and Books tables, filtering for the 'Fiction' genre, counting the number of books per author, and ordering the results as specified.

• Join Authors and Books Tables: Combine the Authors and Books tables based on the book_id to associate each author with their respective books.
• Filter for 'Fiction' Genre: Restrict the dataset to include only those books that belong to the 'Fiction' genre.
• Count Fiction Books per Author: For each author, count the number of distinct 'Fiction' books they have written.
• Order the Results: Sort the final output by fiction_books_count in descending order. In case of a tie, sort by author_name in ascending order.

SQL Query

SELECT A.author_name,
       COUNT(B.book_id) AS fiction_books_count
FROM   Authors A
       JOIN Books B ON A.book_id = B.book_id
WHERE  B.genre = 'Fiction'
GROUP  BY A.author_name
ORDER  BY fiction_books_count DESC, A.author_name ASC;

Step-by-Step Approach

Step 1: Join Authors and Books Tables and Filter for 'Fiction' Genre

Combine the Authors and Books tables to associate each author with their books, and filter the records to include only those books that belong to the 'Fiction' genre.

SQL Query:

SELECT A.author_name, B.book_id
FROM   Authors A
       JOIN Books B ON A.book_id = B.book_id
WHERE  B.genre = 'Fiction';

Explanation:

• SELECT A.author_name, B.book_id:
  • Retrieves the author_name from the Authors table and the corresponding book_id from the Books table.
• FROM Authors A JOIN Books B ON A.book_id = B.book_id:
  • Performs an inner join between the Authors and Books tables based on the book_id, ensuring that only matching records are combined.
• WHERE B.genre = 'Fiction':
  • Filters the joined records to include only those books that are categorized under the 'Fiction' genre.

Output After Step 1:

Assuming the example input provided, the intermediate result after joining and filtering would be:

+---------------------+---------+
| author_name         | book_id |
+---------------------+---------+
| Leo Tolstoy         | 1       |
| Leo Tolstoy         | 2       |
| Fyodor Dostoevsky   | 3       |
| F. Scott Fitzgerald | 4       |
+---------------------+---------+

Step 2: Count Fiction Books per Author

For each author, count the number of distinct 'Fiction' books they have written to determine their fiction_books_count.

SQL Query:

SELECT A.author_name,
       COUNT(B.book_id) AS fiction_books_count
FROM   Authors A
       JOIN Books B ON A.book_id = B.book_id
WHERE  B.genre = 'Fiction'
GROUP  BY A.author_name;

Explanation:

• SELECT A.author_name, COUNT(B.book_id) AS fiction_books_count:

  • Selects each author_name and counts the number of associated book_ids that are in the 'Fiction' genre.

• GROUP BY A.author_name:
  • Groups the results by author_name to perform the count for each individual author.

Output After Step 2:

Based on the intermediate result from Step 1, the aggregated counts per author would be:

+---------------------+---------------------+
| author_name         | fiction_books_count |
+---------------------+---------------------+
| Leo Tolstoy         | 2                   |
| Fyodor Dostoevsky   | 1                   |
| F. Scott Fitzgerald | 1                   |
+---------------------+---------------------+

Step 3: Order the Results by fiction_books_count Descending and author_name Ascending

Sort the final list of authors based on the number of 'Fiction' books they have written in descending order. In cases where authors have the same count, sort them alphabetically by their names in ascending order.

SQL Query:

ORDER  BY fiction_books_count DESC, A.author_name ASC;

Explanation:

• ORDER BY fiction_books_count DESC, A.author_name ASC:
  • fiction_books_count DESC:
    • Orders the authors by their fiction_books_count in descending order, placing authors with more 'Fiction' books at the top.
  • A.author_name ASC:
    • For authors with the same fiction_books_count, orders them alphabetically by author_name in ascending order.

Final Output:

+---------------------+---------------------+
| author_name         | fiction_books_count |
+---------------------+---------------------+
| Leo Tolstoy         | 2                   |
| F. Scott Fitzgerald | 1                   |
| Fyodor Dostoevsky   | 1                   |
+---------------------+---------------------+

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