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Database

3358. Books with NULL Ratings 🔒

中文文档

Description

Table: books

+----------------+---------+
| Column Name    | Type    |
+----------------+---------+
| book_id        | int     |
| title          | varchar |
| author         | varchar |
| published_year | int     |
| rating         | decimal |
+----------------+---------+
book_id is the unique key for this table.
Each row of this table contains information about a book including its unique ID, title, author, publication year, and rating.
rating can be NULL, indicating that the book hasn't been rated yet.

Write a solution to find all books that have not been rated yet (i.e., have a NULL rating).

Return the result table ordered by book_id in ascending order.

The result format is in the following example.

 

Example:

Input:

books table:

+---------+------------------------+------------------+----------------+--------+
| book_id | title                  | author           | published_year | rating |
+---------+------------------------+------------------+----------------+--------+
| 1       | The Great Gatsby       | F. Scott         | 1925           | 4.5    |
| 2       | To Kill a Mockingbird  | Harper Lee       | 1960           | NULL   |
| 3       | Pride and Prejudice    | Jane Austen      | 1813           | 4.8    |
| 4       | The Catcher in the Rye | J.D. Salinger    | 1951           | NULL   |
| 5       | Animal Farm            | George Orwell    | 1945           | 4.2    |
| 6       | Lord of the Flies      | William Golding  | 1954           | NULL   |
+---------+------------------------+------------------+----------------+--------+

Output:

+---------+------------------------+------------------+----------------+
| book_id | title                  | author           | published_year |
+---------+------------------------+------------------+----------------+
| 2       | To Kill a Mockingbird  | Harper Lee       | 1960           |
| 4       | The Catcher in the Rye | J.D. Salinger    | 1951           |
| 6       | Lord of the Flies      | William Golding  | 1954           |
+---------+------------------------+------------------+----------------+

Explanation:

  • The books with book_id 2, 4, and 6 have NULL ratings.
  • These books are included in the result table.
  • The other books (book_id 1, 3, and 5) have ratings and are not included.
The result is ordered by book_id in ascending order

Solutions

Solution 1: Conditional Filtering

We directly filter out books where rating is NULL, then sort them in ascending order by book_id.

Note that the result set should only include the fields book_id, title, author, and published_year.

MySQL

# Write your MySQL query statement below
SELECT book_id, title, author, published_year
FROM books
WHERE rating IS NULL
ORDER BY 1;

Pandas

import pandas as pd


def find_unrated_books(books: pd.DataFrame) -> pd.DataFrame:
    unrated_books = books[books["rating"].isnull()]
    return unrated_books[["book_id", "title", "author", "published_year"]].sort_values(
        by="book_id"
    )