with point_table as(
select *,
       FLOOR(timestampdiff(second,visit_time,leave_time)/600) as single_point 
       # 注意题目的理解，应该是每满10分钟则积1分，满20分钟则积2分，满40分则积4分，是这个意思。
from visit_tb
)

select user_id,
       sum(single_point) as point
from point_table
group by user_id
order by point desc