mysql - 如何获得每月发布或评论的唯一活跃用户数？

Question

我有以下表格：

内容: content_id, user_id, post_date

评论：comment_id、user_id、comment_date

如何获得按月和年分组的活跃唯一用户数？活跃意味着用户在该给定月份发布或评论。

Answer 1

SELECT
  T.action_year,
  T.action_month,
  COUNT(T.user_id) active_users
FROM
  (
  SELECT DISTINCT user_id, YEAR(post_date) action_year, MONTH(post_date) action_month FROM content
  UNION
  SELECT DISTINCT user_id, YEAR(comment_date) action_year, MONTH(comment_date) action_date FROM comment
  ) T
GROUP BY
  T.action_year,
  T.action_month
ORDER BY
  T.action_year ASC,
  T.action_month ASC