Question

我遇到mysql查询问题。我有一个带有ID（自动增量）的表，一个用户ID，一个值和以秒为单位的时间。现在我想得到每个用户的两个最低值的差异，但不知道如何做到：（

我有下表：

id   |  uid  | myvalue |  thetime
-----+-------+---------+-----------
13   |   1   |   120   | 1389287800
14   |   2   |   100   | 1389287810
15   |   3   |   110   | 1389287820
16   |   2   |    80   | 1389287830
17   |   4   |   100   | 1389287840
18   |   1   |   110   | 1389287850
19   |   3   |   105   | 1389287860
20   |   1   |   100   | 1389287870

我希望得到以下结果：

uid  | difference      --> Order by difference
-----+------------
 2   |     20
 1   |     10
 3   |      5

如果有人出去帮助我，那就太好了。非常感谢!!

Answer 1

你必须改进这一点，但这基本上就是你这样做的。你可以使用自我加入

SELECT uid, MAX(myvalue)-MIN(myvalue) AS diff FROM
    (SELECT a.* FROM tablename AS a
        LEFT JOIN tablename AS a2
            ON a.uid=a2.uid AND a.myvalue<=a2.myvalue
        GROUP BY uid,myvalue
        HAVING COUNT(*)<=2
    ) a
GROUP BY uid

为每个用户选择两个最新行以获得列的差异（MySQL）

1 个答案: