mysql - 选择具有 MAX(datetime) 的行并获取列的最小值及其日期？

Question

我的表是这样的(np_capacity):

id  tower  datetime             capacity
---|----|---------------------|----------
1  | A  | 2016-05-29 09:02:41 | 34676
2  | B  | 2016-05-29 09:02:41 | 10736
5  | C  | 2016-05-29 09:02:41 | 55664
3  | D  | 2016-05-29 09:02:41 | 32622
4  | A  | 2016-05-29 13:08:38 | 5474
6  | B  | 2016-05-29 13:08:38 | 20692
7  | C  | 2016-05-29 13:08:38 | 134802
8  | D  | 2016-05-29 13:08:38 | 4754

这是我的查询:

SELECT npc.*,
                (SELECT min(c2.capacity) FROM np_capacity c2 WHERE c2.tower = npc.tower AND datetime BETWEEN (NOW() - INTERVAL 14 DAY) AND NOW()) minCapacity,

                FROM (SELECT max(datetime) maxDatetime FROM np_capacity) c1
                JOIN np_capacity npc ON (npc.datetime = c1.maxDatetime)

它将选择具有最大日期时间的所有塔，然后对于这些塔，它还将选择表中过去两周的最小容量值。输出是这样的:

id  tower  datetime             capacity   MinCapacity
---|----|---------------------|----------|-------------
4  | A  | 2016-05-29 13:08:38 | 5474     | 5474
6  | B  | 2016-05-29 13:08:38 | 20692    | 10736
7  | C  | 2016-05-29 13:08:38 | 134802   | 55664
8  | D  | 2016-05-29 13:08:38 | 4754     | 4754

到目前为止一切都很好。日期时间是 max(datetime) 的，而 MinCapacity 是过去两周的最小值，也是我想要的。如何获取所选 MinCapacity 的具体日期时间。 (最小容量日期)

Answer 1

您可以尝试一下，SQLFiddle 中对此进行了演示。 。如果超过 1 行具有最小容量，则返回最近的日期。

SELECT np_capacity.id, np_capacity.tower, np_capacity.datetime
        ,np_capacity.capacity, mincap.mincapacity
         ,  MAX(tmincapdatetime.datetime) AS datetimeOfMin
FROM (SELECT MAX(`datetime`) AS maxdatetime 
      FROM np_capacity) AS tmaxdatetime
JOIN np_capacity
  ON tmaxdatetime.maxdatetime = np_capacity.`datetime`
LEFT JOIN (SELECT tower, MIN(capacity) as mincapacity
           FROM np_capacity
           WHERE `datetime` BETWEEN (NOW() - INTERVAL 14 DAY) AND NOW()
           GROUP BY tower) AS mincap
  ON mincap.tower = np_capacity.tower  
LEFT JOIN np_capacity AS tmincapdatetime
   ON tmincapdatetime.`datetime` BETWEEN (NOW() - INTERVAL 14 DAY) AND NOW()
      AND mincap.tower = tmincapdatetime.tower
      AND mincap.mincapacity = tmincapdatetime.capacity
GROUP BY np_capacity.id, np_capacity.tower, np_capacity.datetime
  ,np_capacity.capacity, mincap.mincapacity
ORDER BY tower;