我有一个具有以下结构的数据库：

rowid       ID                  startTimestamp   endTimestamp   subject
1           00:50:c2:63:10:1a   ...1000          ...1090        entrance
2           00:50:c2:63:10:1a   ...1100          ...1270        entrance
3           00:50:c2:63:10:1a   ...1300          ...1310        door1
4           00:50:c2:63:10:1a   ...1370          ...1400        entrance
.
.
.

借助此SQL查询，我可以获得一行和下一行之间endTime和startTime之间的平均差异，并按主题和ID进行排序，并带有其最小值，最大值，方差和标准差：

SELECT ID,AVG(diff) AS average,
   AVG(diff*diff) - AVG(diff)*AVG(diff) AS variance,
   SQRT(AVG(diff*diff) - AVG(diff)*AVG(diff)) AS stdev,
   MIN(diff) AS minTime,
   MAX(diff) AS maxTime

FROM
(SELECT t1.id, t1.endTimestamp,
        min(t2.startTimeStamp) - t1.endTimestamp AS diff
FROM table1 t1
INNER JOIN table1 t2
ON t2.ID = t1.ID AND t2.subject = t1.subject
AND t2.startTimestamp > t1.startTimestamp  -- consider only later startTimestamps
WHERE t1.subject = 'entrance'
GROUP BY t1.id, t1.endTimestamp) AS diffs
GROUP BY ID

如果我在同一天只有几行且时差较小，那么这可以很好地工作，您可以在此sqlfiddle中看到它：

http://sqlfiddle.com/#!2/6de73/1

但是当我在另一天有其他数据时，我得到了错误的值：

http://sqlfiddle.com/#!2/920b6/1

因此，我想计算每一天的平均，最小，最大，方差，标准差。

我知道有MySQL的DATE-Functions，但是我做不完…有人可以帮我吗？还是我必须编写一段可以处理此问题的PHP代码？