Question

我有一张名为water_tank的表，

select * from tank_id; 


id  unique_tankId  highLevel    lowLevel
1     1             75          50
2     2             80          55


select * from water_tank where tabkId=1; 


id  tankId  level   serverTimeStamp
1     1     50      2016-06-28 12:00:01
2     1     60      2016-06-28 12:59:01
3     1     85      2016-06-28 13:00:01
4     1     89      2016-06-28 13:30:01
5     1     90      2016-06-28 14:00:01
6     1     100     2016-06-28 15:00:01
7     1     10      2016-06-28 16:00:01
8     1     20      2016-06-28 16:30:01
9     1     28      2016-06-28 17:00:01
10    1     50      2016-06-29 12:00:01
11    1     60      2016-06-29 12:59:01
12    1     67      2016-06-29 13:00:01
13    1     75      2016-06-29 15:00:01
14    1     90      2016-06-29 16:00:01
15    1     95      2016-06-29 17:00:01
16    1     98      2016-06-29 18:00:01
17    1     100     2016-06-29 19:30:01
18    1     24      2016-06-29 20:00:01
..      ..  ..      ...
..      ..  ..      ...

注意： id是AI，tankId是外键

我希望使用mysql查询找到从high（level> = 75）级别serverTimeStamp到low（level＆lt; 50）级别serverTimeStamp的时间差。

期待输出：

timeDiffInHour      highReachedTime         cleanedTime
3                   2016-06-28 13:00:01     2016-06-28 16:00:01
5                   2016-06-29 15:30:01     2016-06-29 20:00:01
..                  ...                     ...

有人帮助我实现这个目标吗？

Answer 1

也许是这样的？

SELECT tankId, 
MIN(serverTimeStamp) lowReachedTime, 
b.highReachedTime,
TIMESTAMPDIFF(HOUR,MIN(serverTimeStamp),b.highReachedTime) timeDiffinHour
FROM tankId a
INNER JOIN (
   SELECT tankId, MAX(serverTimeStamp) highReachedTime 
   FROM water_tank
   WHERE level > 75
   GROUP BY tankId
) b ON b.tankId = a.tankId
WHERE level < 50
GROUP BY a.tankId

mysql - 如何根据从高到低的时间找到时差

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