题解 | 牛客直播开始时各直播间在线人数
牛客直播开始时各直播间在线人数
https://www.nowcoder.com/practice/bdd30e83d47043c99def6d9671bb6dbf
SELECT c.course_id, c.course_name,
COUNT(DISTINCT a.user_id) online_num
FROM course_tb c
JOIN attend_tb a USING(course_id)
WHERE TIME(a.in_datetime) <= '19:00:00'
AND TIME(a.out_datetime) > '19:00:00'
GROUP BY c.course_id, c.course_name
ORDER BY c.course_id
