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Jul 19, 2025
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task: #3570 & All fremium easy completed #78

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1 change: 1 addition & 0 deletions README.md
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Expand Up @@ -159,6 +159,7 @@ Useful for preparing for technical interviews and improving your SQL skills.
- [2356. Number of Unique Subjects Taught by Each Teacher](./leetcode/easy/2356.%20Number%20of%20Unique%20Subjects%20Taught%20by%20Each%20Teacher.sql)
- [3436. Find Valid Emails](./leetcode/easy/3436.%20Find%20Valid%20Emails.sql)
- [3465. Find Products with Valid Serial Numbers](./leetcode/easy/3465.%20Find%20Products%20with%20Valid%20Serial%20Numbers.sql)
- [3570. Find Books with No Available Copies](./leetcode/easy/3570.%20Find%20Books%20with%20No%20Available%20Copies.sql)
2. [Medium](./leetcode/medium/)
- [176. Second Highest Salary](./leetcode/medium/176.%20Second%20Highest%20Salary.sql)
- [180. Consecutive Numbers](./leetcode/medium/180.%20Consecutive%20Numbers.sql)
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59 changes: 59 additions & 0 deletions leetcode/easy/3570. Find Books with No Available Copies.sql
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/*
Question 3570. Find Books with No Available Copies
Link: https://leetcode.com/problems/find-books-with-no-available-copies/description/?envType=problem-list-v2&envId=database

Table: library_books

+------------------+---------+
| Column Name | Type |
+------------------+---------+
| book_id | int |
| title | varchar |
| author | varchar |
| genre | varchar |
| publication_year | int |
| total_copies | int |
+------------------+---------+
book_id is the unique identifier for this table.
Each row contains information about a book in the library, including the total number of copies owned by the library.
Table: borrowing_records

+---------------+---------+
| Column Name | Type |
+---------------+---------+
| record_id | int |
| book_id | int |
| borrower_name | varchar |
| borrow_date | date |
| return_date | date |
+---------------+---------+
record_id is the unique identifier for this table.
Each row represents a borrowing transaction and return_date is NULL if the book is currently borrowed and hasn't been returned yet.
Write a solution to find all books that are currently borrowed (not returned) and have zero copies available in the library.

A book is considered currently borrowed if there exists a borrowing record with a NULL return_date
Return the result table ordered by current borrowers in descending order, then by book title in ascending order.
*/

WITH br AS (
SELECT
book_id,
COUNT(book_id) AS current_borrowers
FROM borrowing_records
WHERE return_date IS NULL
GROUP BY book_id
)

SELECT
lb.book_id,
lb.title,
lb.author,
lb.genre,
lb.publication_year,
br.current_borrowers
FROM library_books AS lb
INNER JOIN
br
ON lb.book_id = br.book_id
WHERE (lb.total_copies - br.current_borrowers) = 0
ORDER BY br.current_borrowers DESC, lb.title ASC