题解 | #牛客直播各科目同时在线人数#
牛客直播各科目同时在线人数
https://www.nowcoder.com/practice/d69677e41f9a4bf3b3ed7a42573e9490
with temp as(
select
user_id,
attend_tb.course_id,
course_name,
in_datetime as dt,
1 as flag
from
attend_tb
left join course_tb on attend_tb.course_id = course_tb.course_id
union all
select
user_id,
attend_tb.course_id,
course_name,
out_datetime as dt,
-1 as flag
from
attend_tb
left join course_tb on attend_tb.course_id = course_tb.course_id
)
select
course_id,course_name,max(num)
from
(
select
course_id,
course_name,
sum(flag) over(
partition by course_id
order by
dt
) as num
from
temp
) t
group by course_id,course_name
order by course_id
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