Mysql 根据异步时间和平均值 JOIN 两个表

Question

我记录了温度和湿度传感器的值，如下所示:

mysql> SELECT date,valeur FROM temperature WHERE date >= NOW() - INTERVAL 2 HOUR;
+---------------------+--------+
| date                | valeur |
+---------------------+--------+
| 2013-09-26 11:30:40 |   25.2 |
| 2013-09-26 11:33:19 |   25.4 |
| 2013-09-26 11:34:12 |   25.5 |
| 2013-09-26 11:38:37 |   25.4 |
| 2013-09-26 11:39:30 |   25.4 |
| 2013-09-26 11:40:23 |   25.4 |
| 2013-09-26 11:43:02 |   25.4 |
| 2013-09-26 11:45:41 |   25.3 |
| 2013-09-26 11:47:33 |   25.3 |
| 2013-09-26 11:51:07 |   25.4 |
| 2013-09-26 11:51:52 |   25.3 |
| 2013-09-26 11:53:38 |   25.4 |
...
| 2013-09-26 12:26:20 |   25.5 |
| 2013-09-26 12:27:12 |   25.5 |
| 2013-09-26 12:32:30 |   25.4 |
| 2013-09-26 12:35:09 |   25.5 |
| 2013-09-26 12:36:02 |   25.5 |
| 2013-09-26 12:37:50 |   25.6 |
| 2013-09-26 12:40:27 |   25.6 |
| 2013-09-26 12:49:18 |   25.6 |
| 2013-09-26 12:52:54 |   25.6 |
...
| 2013-09-26 13:16:40 |   25.5 |
| 2013-09-26 13:17:33 |   25.6 |
| 2013-09-26 13:22:05 |   25.5 |
| 2013-09-26 13:22:51 |   25.5 |
| 2013-09-26 13:23:44 |   25.5 |
| 2013-09-26 13:24:37 |   25.5 |
| 2013-09-26 13:25:30 |   25.5 |
| 2013-09-26 13:28:09 |   25.6 |
+---------------------+--------+

mysql> SELECT date,valeur FROM humidite WHERE date >= NOW() - INTERVAL 2 HOUR;
+---------------------+--------+
| date                | valeur |
+---------------------+--------+
| 2013-09-26 11:30:40 |     78 |
| 2013-09-26 11:33:19 |     78 |
| 2013-09-26 11:34:12 |     78 |
| 2013-09-26 11:38:37 |     78 |
| 2013-09-26 11:39:30 |     78 |
| 2013-09-26 11:40:23 |     78 |
| 2013-09-26 11:43:02 |     79 |
| 2013-09-26 11:45:41 |     78 |
| 2013-09-26 11:47:33 |     78 |
| 2013-09-26 11:51:07 |     79 |
| 2013-09-26 11:51:52 |     79 |
| 2013-09-26 11:53:38 |     79 |
...
| 2013-09-26 12:22:48 |     78 |
| 2013-09-26 12:26:20 |     78 |
| 2013-09-26 12:27:12 |     78 |
| 2013-09-26 12:32:30 |     77 |
| 2013-09-26 12:35:09 |     77 |
| 2013-09-26 12:36:02 |     77 |
| 2013-09-26 12:37:50 |     78 |
| 2013-09-26 12:40:27 |     77 |
| 2013-09-26 12:43:06 |     78 |
| 2013-09-26 13:22:05 |     78 |
...
| 2013-09-26 13:22:51 |     78 |
| 2013-09-26 13:23:44 |     78 |
| 2013-09-26 13:24:37 |     78 |
| 2013-09-26 13:25:30 |     78 |
| 2013-09-26 13:28:09 |     78 |
+---------------------+--------+

来自this post我使用这个 mysql 命令连接两个表，并从 24 小时开始每小时获取一个值:

SELECT DATE_FORMAT(timeTable.minuteTime, '%Y-%m-%d %k:%i') date,
T2.valeur temp,
P2.valeur hum
FROM
(
    SELECT minuteTime.minuteTime minuteTime,
    ( SELECT MAX(date) FROM temperature WHERE date <= minuteTime.minuteTime AND date >= NOW() - INTERVAL 1 DAY) tempTime,
    ( SELECT MAX(date) FROM humidite WHERE date <= minuteTime.minuteTime AND date >= NOW() - INTERVAL 1 DAY) humTime
    FROM
    (
        SELECT DATE(date) + INTERVAL (HOUR(date) DIV 1 * 1) HOUR minuteTime
        FROM humidite
        WHERE date >= NOW() - INTERVAL 1 DAY AND date <= NOW()
        UNION SELECT DATE(date) + INTERVAL (HOUR(date) DIV 1 * 1) HOUR
        FROM temperature
        WHERE date >= NOW() - INTERVAL 1 DAY AND date <= NOW()
        GROUP BY 1
    ) minuteTime
) timeTable
LEFT JOIN temperature T2 ON T2.date = timeTable.tempTime
LEFT JOIN humidite P2 ON P2.date = timeTable.humTime
ORDER BY minuteTime ASC;

它工作得很好，但我真的不明白如何选择该值(在区间内随机？)。我更喜欢每小时的平均值:

+------------------+------+------+
| date             | temp | hum  |
+------------------+------+------+
| 2013-09-25 13:00 | NULL | NULL |
| 2013-09-25 14:00 | 25.1 |   80 |
| 2013-09-25 15:00 | 25.3 |   78 |
| 2013-09-25 16:00 | 25.6 |   75 |
| 2013-09-25 17:00 | 25.5 |   75 |
| 2013-09-25 18:00 | 25.0 |   78 |
| 2013-09-25 19:00 | 24.2 |   80 |
| 2013-09-25 20:00 | 23.9 |   84 |
| 2013-09-25 21:00 | 23.9 |   84 |
| 2013-09-25 22:00 | 24.1 |   83 |
| 2013-09-25 23:00 | 24.1 |   83 |
| 2013-09-26 0:00  | 24.0 |   82 |
| 2013-09-26 1:00  | 23.9 |   84 |
| 2013-09-26 2:00  | 23.7 |   86 |
| 2013-09-26 3:00  | 23.7 |   84 |
| 2013-09-26 4:00  | 23.7 |   85 |
| 2013-09-26 5:00  | 23.4 |   85 |
| 2013-09-26 6:00  | 23.6 |   85 |
| 2013-09-26 7:00  | 23.7 |   85 |
| 2013-09-26 8:00  | 24.0 |   84 |
| 2013-09-26 9:00  | 24.4 |   82 |
| 2013-09-26 10:00 | 24.6 |   81 |
| 2013-09-26 11:00 | 25.2 |   79 |
| 2013-09-26 12:00 | 25.4 |   79 |
| 2013-09-26 13:00 | 25.6 |   78 |
+------------------+------+------+
25 rows in set (1.11 sec)

你知道如何将 AVG() 放入这段代码中吗？

额外问题:我更改了代码以获取每小时一个值。你知道如何每 30 分钟获取 1 个值吗？

感谢您的帮助

Answer 1

试试这个:

select FROM_UNIXTIME( TRUNCATE(UNIX_TIMESTAMP(timeTable.minuteTime) / 1800,0)*1800) as halfHour,
avg(T2.valeur) as avgTemp,
avg(P2.valeur) as avgHum
FROM
(
    SELECT minuteTime.minuteTime minuteTime,
    ( SELECT MAX(date) FROM temperature WHERE date <= minuteTime.minuteTime AND date >= NOW() - INTERVAL 1 DAY) tempTime,
    ( SELECT MAX(date) FROM humidite WHERE date <= minuteTime.minuteTime AND date >= NOW() - INTERVAL 1 DAY) humTime
    FROM
    (
        SELECT DATE(date) + INTERVAL (HOUR(date) DIV 1 * 1) HOUR minuteTime
        FROM humidite
        WHERE date >= NOW() - INTERVAL 1 DAY AND date <= NOW()
        UNION SELECT DATE(date) + INTERVAL (HOUR(date) DIV 1 * 1) HOUR
        FROM temperature
        WHERE date >= NOW() - INTERVAL 1 DAY AND date <= NOW()
        GROUP BY 1
    ) minuteTime
) timeTable
LEFT JOIN temperature T2 ON T2.date = timeTable.tempTime
LEFT JOIN humidite P2 ON P2.date = timeTable.humTime
group by FROM_UNIXTIME( TRUNCATE(UNIX_TIMESTAMP(timeTable.minuteTime) / 1800,0)*1800)
ORDER BY 1 ASC;