Question

假设我有这个问题：

SELECT report_id, time_sent
FROM  report_submissions
WHERE report_id IN (1,2,3,4,5,6)
ORDER BY report_id ASC, time_sent DESC

有了这个结果：

report_id   time_sent
1           2
1           1
2           4
2           3
3           4

我想更改该查询，以便获得带有max（time_sent）的DISTINCT report_id，例如：

report_id   time_sent
1           2
2           4
3           4

如何以最有效的方式实现这一目标？感谢。

Answer 1

SELECT report_id, max(time_sent)
FROM  report_submissions
WHERE report_id IN (1,2,3,4,5,6)
GROUP BY report_id
ORDER BY report_id ASC

Answer 2

DISTINCT是一个懒惰的GROUP BY！

SELECT report_id, max(time_sent)
FROM  report_submissions
WHERE report_id IN (1,2,3,4,5,6)
GROUP BY report_id
ORDER BY report_id ASC, max(time_sent) DESC

Answer 3

您需要使用group by

请参阅：http://dev.mysql.com/doc/refman/5.0/en/group-by-functions.html

MySQL在一列上与其他最大列不同

3 个答案: