LeetCode(1407)排名靠前的旅行者

注意

1：

left join 用的是on而不是where

2:

如果空则赋0

ifnull(sum(r.distance,0)

select u.name name,ifnull(sum(r.distance),0) travelled_distance from Users u left join Rides r on u.id=r.user_id group by user_id order by travelled_distance desc,name;