MySQL show sum of difference of two values

Question

Below is my query.

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`) AS kwh_dif         


        

Answer 1

You can’t use window functions within an aggregate function (while the opposite is possible), Here, you need to use a subquery, and aggregate in the outer query:

SELECT name, customer_id, SUM(kwh_diff) sum_kwh_diff
FROM (
    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`) AS kwh_diff
    FROM mdc_node n
    INNER JOIN `mdc_meters_data` m ON n.`customer_id` = m.`cust_id`
    WHERE n.`lft` = 5 AND n.`icon` NOT IN ('folder')
    AND m.`data_date_time` BETWEEN NOW() - INTERVAL 30 DAY AND NOW()
) t
GROUP BY name, customer_id