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133 lines
5.7 KiB
HTML
133 lines
5.7 KiB
HTML
<p>Table: <code>library_books</code></p>
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<pre>
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+------------------+---------+
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| Column Name | Type |
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+------------------+---------+
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| book_id | int |
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| title | varchar |
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| author | varchar |
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| genre | varchar |
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| publication_year | int |
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| total_copies | int |
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+------------------+---------+
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book_id is the unique identifier for this table.
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Each row contains information about a book in the library, including the total number of copies owned by the library.
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</pre>
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<p>Table: <code>borrowing_records</code></p>
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<pre>
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+---------------+---------+
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| Column Name | Type |
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+---------------+---------+
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| record_id | int |
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| book_id | int |
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| borrower_name | varchar |
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| borrow_date | date |
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| return_date | date |
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+---------------+---------+
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record_id is the unique identifier for this table.
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Each row represents a borrowing transaction and return_date is NULL if the book is currently borrowed and hasn't been returned yet.
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</pre>
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<p>Write a solution to find <strong>all books</strong> that are <strong>currently borrowed (not returned)</strong> and have <strong>zero copies available</strong> in the library.</p>
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<ul>
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<li>A book is considered <strong>currently borrowed</strong> if there exists a<strong> </strong>borrowing record with a <strong>NULL</strong> <code>return_date</code></li>
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</ul>
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<p>Return <em>the result table ordered by current borrowers in <strong>descending</strong> order, then by book title in <strong>ascending</strong> order.</em></p>
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<p>The result format is in the following example.</p>
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<p> </p>
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<p><strong class="example">Example:</strong></p>
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<div class="example-block">
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<p><strong>Input:</strong></p>
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<p>library_books table:</p>
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<pre class="example-io">
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+---------+------------------------+------------------+----------+------------------+--------------+
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| book_id | title | author | genre | publication_year | total_copies |
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+---------+------------------------+------------------+----------+------------------+--------------+
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| 1 | The Great Gatsby | F. Scott | Fiction | 1925 | 3 |
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| 2 | To Kill a Mockingbird | Harper Lee | Fiction | 1960 | 3 |
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| 3 | 1984 | George Orwell | Dystopian| 1949 | 1 |
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| 4 | Pride and Prejudice | Jane Austen | Romance | 1813 | 2 |
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| 5 | The Catcher in the Rye | J.D. Salinger | Fiction | 1951 | 1 |
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| 6 | Brave New World | Aldous Huxley | Dystopian| 1932 | 4 |
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+---------+------------------------+------------------+----------+------------------+--------------+
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</pre>
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<p>borrowing_records table:</p>
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<pre class="example-io">
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+-----------+---------+---------------+-------------+-------------+
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| record_id | book_id | borrower_name | borrow_date | return_date |
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+-----------+---------+---------------+-------------+-------------+
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| 1 | 1 | Alice Smith | 2024-01-15 | NULL |
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| 2 | 1 | Bob Johnson | 2024-01-20 | NULL |
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| 3 | 2 | Carol White | 2024-01-10 | 2024-01-25 |
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| 4 | 3 | David Brown | 2024-02-01 | NULL |
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| 5 | 4 | Emma Wilson | 2024-01-05 | NULL |
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| 6 | 5 | Frank Davis | 2024-01-18 | 2024-02-10 |
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| 7 | 1 | Grace Miller | 2024-02-05 | NULL |
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| 8 | 6 | Henry Taylor | 2024-01-12 | NULL |
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| 9 | 2 | Ivan Clark | 2024-02-12 | NULL |
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| 10 | 2 | Jane Adams | 2024-02-15 | NULL |
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+-----------+---------+---------------+-------------+-------------+
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</pre>
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<p><strong>Output:</strong></p>
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<pre class="example-io">
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+---------+------------------+---------------+-----------+------------------+-------------------+
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| book_id | title | author | genre | publication_year | current_borrowers |
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+---------+------------------+---------------+-----------+------------------+-------------------+
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| 1 | The Great Gatsby | F. Scott | Fiction | 1925 | 3 |
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| 3 | 1984 | George Orwell | Dystopian | 1949 | 1 |
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+---------+------------------+---------------+-----------+------------------+-------------------+
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</pre>
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<p><strong>Explanation:</strong></p>
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<ul>
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<li><strong>The Great Gatsby (book_id = 1):</strong>
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<ul>
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<li>Total copies: 3</li>
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<li>Currently borrowed by Alice Smith, Bob Johnson, and Grace Miller (3 borrowers)</li>
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<li>Available copies: 3 - 3 = 0</li>
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<li>Included because available_copies = 0</li>
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</ul>
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</li>
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<li><strong>1984 (book_id = 3):</strong>
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<ul>
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<li>Total copies: 1</li>
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<li>Currently borrowed by David Brown (1 borrower)</li>
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<li>Available copies: 1 - 1 = 0</li>
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<li>Included because available_copies = 0</li>
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</ul>
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</li>
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<li><strong>Books not included:</strong>
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<ul>
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<li>To Kill a Mockingbird (book_id = 2): Total copies = 3, current borrowers = 2, available = 1</li>
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<li>Pride and Prejudice (book_id = 4): Total copies = 2, current borrowers = 1, available = 1</li>
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<li>The Catcher in the Rye (book_id = 5): Total copies = 1, current borrowers = 0, available = 1</li>
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<li>Brave New World (book_id = 6): Total copies = 4, current borrowers = 1, available = 3</li>
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</ul>
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</li>
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<li><strong>Result ordering:</strong>
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<ul>
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<li>The Great Gatsby appears first with 3 current borrowers</li>
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<li>1984 appears second with 1 current borrower</li>
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</ul>
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</li>
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</ul>
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<p>Output table is ordered by current_borrowers in descending order, then by book_title in ascending order.</p>
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</div>
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