Mysql 在特定日期，使用sql/PHP计算两个不同行/列中两个数字的平均值、方差和标准偏差

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
.
.
.

通过此SQL查询，我可以获得一行和下一行之间的endTime和startTime之间的平均差异，按主题和ID排序，以及它们的最小值、最大值、方差和标准偏差：

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

这很好，如果我在同一天只有几行，时差较小，您可以在这个sqlfiddle中看到它：

但是，当我在不同的一天有额外的数据时，我得到了不好的值：

因此，我想计算每一天的平均值、最小值、最大值、方差、标准差

---

我知道MySQL有日期函数，但我无法完成…有人能帮我吗？或者我必须编写一段PHP代码来处理这个问题吗？

是否与通过将日期添加到

组一样简单。以下是MySQL和SQLite中都应该使用的语法，以结束时间为基础，并假设结束时间存储为日期时间：

SELECT ID, thedate, 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, DATE(endtimestamp) as thedate,
             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, thedate

如果存储为时间戳，请参阅Marty的评论。
鉴于MySQL具有用于标准偏差和方差的函数，有没有理由不使用它们？是MySQL还是SQLite，还是两者都有？我更喜欢SQLite中的解决方案……但如果我尝试切换，SQLiteFIDLE总是返回错误……如果使用
DATE（FROM_UNIXTIME（endtimestamp））按日期
运行。@MartyMcVry。谢谢你的澄清。嗨，我又做了一把小提琴：看起来很不错……我会在晚上检查这些数值，然后再写一次……@MichaelMeier。你可能想过滤掉从一天开始到另一天结束的任何东西。如果您知道合理性阈值，那么只需添加一个
where
子句，如
where diff<100000
或其他任何内容。@MichaelMeier。我不知道你所说的“差异量”是什么意思。三个概念是
sum（diff）
，
sum（abs（diff））
和
计数（distinct diff）
。