Getting sum of two rows in an inner joined table

Question

I have these two tables;

1. trips

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

2. expenses

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

I would like to get the sum of revenue collected in a day AND sum of expenses in a day. I have the following sql which gives me results but the sums are entirely wrong.

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

Answer 1

You can preaggregate the expenses by trip, and then aggregate again in the outer query:

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