特定の日付のsql/PHPを使用して、2つの異なる行/列の2つの数値の平均、分散、および標準偏差を計算します

日付をgroup byに追加するのと同じくらい簡単ですか 。これは、MySQLとSQLiteの両方で機能する構文であり、終了時刻に基づいて終了時刻が日時として格納されていると想定しています。

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

タイムスタンプとして保存されている場合は、マーティのコメントを参照してください。