题解 | #某滴出行2021年9月各城市每天的快车订单量#

select city_name,a.dt,count(distinct order_id) as flash_count
from order_info_tb a
left join driver_tb b on a.driver_id=b.driver_id
left join city_tb c on b.city_id=c.city_id
where month(a.dt)=9 and a.product_line_id=2
group by b.city_id,a.dt;