如何计算 MySQL 中的累计和

Question

我正在准备面试，在练习最近在亚马逊上提出的一些 SQL 问题时遇到了这个问题。虽然我找不到 table，但问题如下：

查找过去 6 个月西雅图客户的前 10 大最有利table 产品的累计总和。

解决此类查询的方法看起来正确吗？如果没有，解决这个问题的最佳方法是什么？

SELECT t.day,
       t.product_count,
       @running_total:=@running_total + t.product_count AS cumulative_sum
FROM
( SELECT
  date(purchase_date) as day,
  count(product_id) as product_count
  FROM products
  where day > DATE_SUB(now(), INTERVAL 6 MONTH)
  AND customer_city = 'Seattle'
  GROUP BY day 
  ORDER BY product_count desc) t
JOIN (SELECT @running_total:=0) r
ORDER BY t.day
LIMIT 10;

Answer 1

使用这个

select day,product_count,
sum(product_count) over (order by t.day ROWS UNBOUNDED PRECEDING) as cumulative_sum from (
SELECT
  date(purchase_date) as day,
  count(product_id) as product_count
  FROM products
  where day > DATE_SUB(now(), INTERVAL 6 MONTH)
  AND customer_city = 'Seattle'
  GROUP BY day 
  ORDER BY product_count desc
)t

如何计算 MySQL 中的累计和

How to calculate cumulative sums in MySQL

mysql

sql

group-by

cumulative-sum