php - 使用 sqlite/php 获取两个不同行/列中两个数字的差异

Question

我有一个带有名为“events”的表的 SQLite 数据库，它具有以下结构:

rowid       ID                  startTimestamp   endTimestamp
1           00:50:c2:63:10:1a   1000             1010
2           00:50:c2:63:10:1a   1100             1030
3           00:50:c2:63:10:1a   1090             1110   
4           00:50:c2:63:10:1a   1210             1310
.
.
.

计算startTimestamp和endTimestamp之间的平均时间没有问题:

SELECT ID, avg(endTimestamp - startTimestamp) AS duration FROM events WHERE senderID ="00:50:c2:63:10:1a"

但现在我想计算一行和下一行之间的 endTime 和 startTime 之间的平均差异，这对于我的示例来说意味着:

1100-1010 = 90

1090-1030 = 60

1210-1110 = 100

---

差异总和 = 90 + 60 + 100 = 250

平均差异 = 250/3 = 83,33

有没有办法用 SQL 查询来做到这一点？还是有必要用PHP写一段代码？

Answer 1

SELECT
    id,
    ( MAX(endtimestamp) - MIN(startTimestamp)
    - SUM(endtimestamp-startTimestamp)
    ) / (COUNT(*)-1) AS averageDifference
FROM
    events
GROUP BY
    id ;

在 SQL-Fiddle 测试: test-1 (感谢@bonCodigo)

---

由于 MIN(endtimestamp) 可能不是具有最低 rowid 的那一个，以上查询需要更正:

SELECT
    id,
    ( ( SELECT endtimestamp FROM events AS ee 
        WHERE ee.id = e.id ORDER BY rowid ASC LIMIT 1 )
    - ( SELECT startTimestamp FROM events AS ee
        WHERE ee.id = e.id ORDER BY rowid DESC LIMIT 1 )
    - SUM(endtimestamp-startTimestamp)
    ) / (COUNT(*)-1) AS averageDifference
FROM
    events AS e
GROUP BY
    id ;