php - 如何计算特定组的多个时间戳值的时差？

Question

+------+--------+---------------------+
| name | status | timecode            |
| U    | ON     | 2013-09-08 00:11:40 |
| A    | OFF    | 2013-09-08 00:12:29 |
| W1   | ON     | 2013-09-08 00:35:29 |
| C    | ON     | 2013-09-08 01:35:37 |
| C    | OFF    | 2013-09-08 02:12:29 |
| G2   | ON     | 2013-09-08 02:35:55 |
| C    | ON     | 2013-09-08 03:19:29 |
| J    | ON     | 2013-09-08 03:35:20 |
| W2   | ON     | 2013-09-08 04:26:31 |
| M    | ON     | 2013-09-08 04:44:23 |
| A    | ON     | 2013-09-08 05:19:29 |
| C    | OFF    | 2013-09-08 05:48:50 |
| W1   | OFF    | 2013-09-08 05:55:55 |
| M    | OFF    | 2013-09-08 06:32:29 |
| U    | OFF    | 2013-09-08 06:52:49 |
| J    | OFF    | 2013-09-08 08:12:29 |
| W2   | ON     | 2013-09-08 08:19:29 |
| G2   | OFF    | 2013-09-08 09:12:29 |
| W2   | OFF    | 2013-09-08 09:26:39 |
| Ma   | ON     | 2013-09-08 09:35:20 |
| C    | ON     | 2013-09-08 09:57:28 |
| J    | ON     | 2013-09-08 10:19:29 |
| Gw   | ON     | 2013-09-08 10:35:20 |
| A    | OFF    | 2013-09-08 11:48:50 |
| G2   | ON     | 2013-09-08 15:19:55 |
| W2   | OFF    | 2013-09-08 15:28:17 |
| G2   | OFF    | 2013-09-08 16:48:38 |
| W1   | ON     | 2013-09-08 18:10:44 |
| Gw   | OFF    | 2013-09-08 20:12:29 |
| W1   | OFF    | 2013-09-08 20:44:18 |
| Ma   | OFF    | 2013-09-08 21:12:29 |
| U    | ON     | 2013-09-08 23:15:59 |
+------+--------+---------------------+

以上是一组传感器的数据，这些传感器在一天中的不同时间打开和关闭。我想计算每个传感器每天打开多少小时。我知道如何获得两次之间的差异，但是如何将每个 ON 与 OFF 配对。有时，其中一个传感器可能会跳过读数并丢弃 ON 或 OFF，因此必须丢弃这些传感器

最好的选择是使用临时表、连接还是变量？我需要在页面上打印结果。

Answer 1

 SELECT x.* 
      , MIN(y.timecode) pair
      , SEC_TO_TIME(TIME_TO_SEC(MIN(y.timecode))-TIME_TO_SEC(x.timecode)) diff
   FROM my_table x
   JOIN my_table y
     ON y.name = x.name
    AND y.status <> x.status
    AND y.timecode > x.timecode
  WHERE x.status = 'ON'
  GROUP
     BY x.name
      , x.timecode;