select
    courier_id,
    courier_name,
    base_salary + coalesce(sum(delivery_fee),0) total_income
from
    couriers_info s1
left join
    deliveries_info s2
using(courier_id)
where date_format(delivery_date,'%y%m') = 2407
group by 1,2,base_salary
order by 1

比低分题解用distinct的好用。group by 效率比distinct高了不知道多少