Sql查询没有返回最大值

Question

我编写了以下查询以获取max issue_id的值。但是我得到了book_id的issue_id 14.我想要的是当book_id为2时获得iss​​ue_id 16.而当book_id为3时，issue_id为15，依此类推。

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获得最高值

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