SQL查詢未返回最大值

Question

我編寫了以下查詢，以獲取具有最大issue_id的值。 但是我獲得book_id 2的issue_id14。我想要的是在book_id為2時獲得iss​​ue_id16。在book_id為3時獲得iss​​ue_id 15，依此類推。

SELECT issue.issue_id AS issue_id, issue.issue_date, issue.student_id, books.availability,
    CASE WHEN NOW() > DATE_ADD(issue.issue_date, INTERVAL 20 DAY)
        THEN 10*DATEDIFF(NOW(), DATE_ADD(issue.issue_date, INTERVAL 20 DAY))
        ELSE 0 END AS fine_amount
        FROM issue
        INNER JOIN books
        ON issue.book_id=books.book_id
        WHERE books.book_id=2 
        HAVING MAX(issue.issue_id)

Answer 1

使用ORDER BY .. LIMIT 1獲得最大值

SELECT issue.issue_id AS issue_id, issue.issue_date, issue.student_id, books.availability,
    CASE WHEN NOW() > DATE_ADD(issue.issue_date, INTERVAL 20 DAY)
        THEN 10*DATEDIFF(NOW(), DATE_ADD(issue.issue_date, INTERVAL 20 DAY))
        ELSE 0 END AS fine_amount
        FROM issue
        INNER JOIN books
        ON issue.book_id=books.book_id
        WHERE books.book_id=2 
        ORDER BY issue.issue_id DESC LIMIT 1