MySQL 获取减法的返回值

Question

我们正在尝试通过使用传感器数据上的时间戳来获取体育锻炼的长度。

我们目前有以下查询:

SELECT UNIX_TIMESTAMP(
    SELECT HAAS2.trainingsdata.timestamp
    FROM HAAS2.trainingdata
    WHERE HAAS2.trainingsdata.training_id= 1
    ORDER BY timestamp DESC LIMIT 1)
- UNIX_TIMESTAMP(
    SELECT HAAS2.trainingsdata.timestamp
    FROM HAAS2.trainingdata
    WHERE HAAS2.trainingsdata.training_id= 1
    ORDER BY timestamp ASC LIMIT 1)
AS output

(为便于阅读而添加的内容)

在 phpMyAdmin 中测试此查询时，我们收到以下错误:

#1064 - You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'SELECT HAAS2.trainingsdata.timestamp FROM HAAS2.trainingdata WHERE HAAS2.trainin' at line 1

我们尝试了不同的方法来记录查询，但都导致了同样的错误。我们不明白语法错误在哪里。

Answer 1

SELECT max(UNIX_TIMESTAMP(timestamp)) -
       min(UNIX_TIMESTAMP(timestamp)) AS output
FROM HAAS2.trainingdata
WHERE training_id = 1