SQL163 每篇文章同一时刻最大在看人数

SELECT
artical_id,
MAX(p_num) AS max_uv

    FROM(
    SELECT
    artical_id,
    mark,
    SUM(mark) OVER(PARTITION BY artical_id ORDER BY time , mark DESC) AS p_num

    FROM(
        SELECT  
        artical_id,
        in_time AS time,
        1 AS mark 
        FROM tb_user_log AS u1
        WHERE artical_id <> '0'
	
        UNION ALL
    
        SELECT 
        artical_id,
        out_time AS time,
        '-1 AS mark 
        FROM tb_user_log AS u2
        WHERE artical_id <> '0') AS a) AS b
        
GROUP BY artical_id

ORDER BY max_uv DESC