获取内部连接表中两行的总和答案

【问题标题】：Getting sum of two rows in an inner joined table获取内部连接表中两行的总和
【发布时间】：2021-03-29 18:39:47
【问题描述】：

我有这两张表；

旅行

id	date	revenue
1	01/01/2020	5000
2	01/01/2020	3000
3	02/01/2020	4000
4	02/01/2020	2000

费用

id	tripid	amount
1	1	500
2	1	300
3	2	400
4	2	200
5	2	700

我想得到一天内收取的收入总和和一天内的费用总和。我有以下 sql，它给了我结果，但总和完全错误。

SELECT i.id, sum(i.revenue) as total, i.date trip , sum(c.amount) as exp, c.tripid expenses FROM trip i INNER JOIN expenses c ON i.id = c.tripid GROUP BY i.date ORDER BY trip DESC

【问题讨论】：

见meta.stackoverflow.com/questions/333952/…

标签： mysql sql sum left-join aggregate-functions

【解决方案1】：

您可以按行程预先聚合费用，然后在外部查询中再次聚合：

select t.date, sum(t.revenue) as revenue, coalesce(sum(e.expense), 0) as expense
from trips t
left join (
    select tripid, sum(amount) as expense
    from expenses
    group by tripid
) e on e.tripid = t.id
group by t.date

【讨论】：