MySQL取两个字段之间的差异

Posted 2023-03-31

【中文标题】MySQL取两个字段之间的差异

【英文标题】：MySQL take difference between two fields

【发布时间】：2020-06-27 05:32:23

【问题描述】：

我有一个从中获取数据的查询。

SELECT n.`name`,n.`customer_id`,m.`msn`, m.kwh FROM mdc_node n
INNER JOIN `mdc_meters_data` m ON n.`customer_id` = m.`cust_id`
WHERE n.`lft` = 3 AND n.`icon` NOT IN ('folder')
AND m.`data_date_time` BETWEEN NOW() - INTERVAL 30 DAY AND NOW()

输出

现在我要做的是减去kwh 的值，例如kwh[2] - kwh[1]、kwh[3] - kwh[2]、kwh[4] - kwh[3].....kwh[n+1] - kwh[n]

任何帮助将不胜感激。

【参考方案1】：

LAG()窗口函数可以用来解决这个问题，如下图，

SELECT n.`name`,n.`customer_id`,m.`msn`, m.kwh,
       m.kwh - LAG(m.kwh) OVER(PARTITION BY n.`customer_id` ORDER BY m.`data_date_time`)
FROM mdc_node n
INNER JOIN `mdc_meters_data` m ON n.`customer_id` = m.`cust_id`
WHERE n.`lft` = 3 AND n.`icon` NOT IN ('folder')
AND m.`data_date_time` BETWEEN NOW() - INTERVAL 30 DAY AND NOW()

【讨论】：

我又发了一个question你能看看吗？