如何利用 MySQL 查询计算出每篇文章被哪些人浏览过，并统计这些浏览者阅读的其他文章的浏览次数，并输出浏览次数最多的前几篇文章？

select
  l.content_id as l_content_id,
  t.content_id as t_content_id,
  count(t.uid) as pv
from read_log as t
join (
  select
    content_id,
    group_concat(distinct uid, '') as uid_list
  from read_log
  group by
    content_id
) as l
  on find_in_set(t.uid, l.uid_list)
group by
  l.content_id,
  t.content_id
order by
  l.content_id,
  pv desc;

SELECT
  l_content_id,
  t_content_id,
  pv
FROM (
  SELECT
    data.*,
#    换这行  data.l_content_id = @last_data_id,
    CASE
      WHEN data.l_content_id = @last_data_id THEN @rank := @rank + 1
      ELSE @rank := 1
    END,
    @rank AS r,
    @last_data_id := data.l_content_id
  FROM (
    SELECT
      l.content_id AS l_content_id,
      --   l.uid_list
      t.content_id AS t_content_id,
      COUNT(t.uid) AS pv
    FROM read_log AS t
    JOIN (
      SELECT
        content_id,
        GROUP_CONCAT(DISTINCT uid, '') AS uid_list
      FROM read_log
      GROUP BY
        content_id
    ) AS l
      ON FIND_IN_SET(t.uid, l.uid_list)
    GROUP BY
      l.content_id,
      t.content_id
    ORDER BY
      l.content_id,
      pv DESC
  ) AS data,
  (SELECT @last_data_id := NULL, @rank := 0) AS tmp
) AS a
WHERE
  r < 4;