Question

我希望在我的数据中获得一小时前的最新旧值，但是当我执行此查询时

SELECT locid, value
FROM  table2
WHERE date_sub(t_stamp, interval 1 hour) 
and locid = '2815'
order by t_stamp desc

我得到了所有的价值观。我该如何解决这个问题？

输出应为

locid  | value
2815   | 13.0

以下是演示：http://sqlfiddle.com/#!2/b3c89/5

Answer 1

以下查询将获取当前小时并从中减去一小时，然后将其与t_stamp小时进行比较。

SELECT locid, value
FROM  table2
WHERE DATE(t_stamp) = DATE(CURRENT_DATE)
AND HOUR(t_stamp) = HOUR(CURRENT_TIME) -1
AND locid = '2815'
ORDER BY t_stamp desc
LIMIT 1

或者您可能正在寻找以下查询：

SELECT locid, value
FROM  table2
WHERE t_stamp <= DATE_SUB(NOW(), INTERVAL 1 HOUR)
AND locid = '2815'
ORDER BY t_stamp desc
LIMIT 1

Answer 2

只需在查询中添加LIMIT即可返回第一行。

SELECT locid, value
FROM  table2
WHERE date_sub(t_stamp, interval 1 hour) 
and locid = '2815'
order by t_stamp desc limit 1

Answer 3

使用LIMIT 1仅返回最高值

从一小时前在mysql中获取最新的旧值

3 个答案: