select r.room_id,r.room_name,count(distinct u.user_id) as user_count
from user_view_tb u join room_info_tb r on u.room_id=r.room_id
where u.in_time < '24:00:00' AND u.out_time > '23:00:00'
group by r.room_id,r.room_name
order by user_count desc

这题我觉得思路不难，主要是人数这里要去重！

其次就是where后面跟的条件如何写