[英]Sql query not returning max value
我编写了以下查询,以获取具有最大issue_id的值。 但是我获得book_id 2的issue_id14。我想要的是在book_id为2时获得issue_id16。在book_id为3时获得issue_id 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)
使用ORDER BY .. LIMIT 1获得最大值
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
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