Question

我有一张表posts，如下所示：

id    | user_id | created_at

我想要一个查询，该查询返回当天最近60天内每天发布的不同用户数。所以结果看起来像是：

date       | count
2017-12-9  | 28
2017-12-10 | 25 (there were 25 different users posting during the previous 60 days to 2017-12-10)

我在MySQL中尝试使用相关子查询，但无论我尝试哪些索引，性能都很糟糕。我当前的查询如下：

SELECT
  DATE(orig_posts.created_at) as date,
  (
    SELECT
        COUNT(DISTINCT(posts.user_id))
    FROM
        posts
    WHERE
        posts.created_at BETWEEN (orig_posts.created_at - INTERVAL 60 DAY) AND orig_posts.created_at
  ) as count
FROM
  posts as orig_posts
WHERE
  orig_posts.created_at > NOW() - INTERVAL 5 DAY
GROUP BY
  DATE(orig_posts.created_at)

在解释查询之后，罪魁祸首似乎是COUNT(DISTINCT(user_id))，但我无法想出这个查询的更好的替代方案。解释输出是：

+----+--------------------+---------------+-------+------------------------------------------------------------------------------------+----------------+---------+------+--------+-----------------------------------------------------------+
| id | select_type        | table         | type  | possible_keys                                                                      | key            | key_len | ref  | rows   | Extra                                                     |
+----+--------------------+---------------+-------+------------------------------------------------------------------------------------+----------------+---------+------+--------+-----------------------------------------------------------+
|  1 | PRIMARY            | orig_posts    | range | created_at_idx,created_at_plus_type_idx,created_at_plus_type_plus_user_id_idx      | created_at_idx | 5       | NULL |  12179 | Using where; Using index; Using temporary; Using filesort |
|  2 | DEPENDENT SUBQUERY | posts         | ALL   | created_at_idx,created_at_plus_type_idx,created_at_plus_type_plus_user_id_idx      | NULL           | NULL    | NULL | 548653 | Range checked for each record (index map: 0x580)          |
+----+--------------------+---------------+-------+------------------------------------------------------------------------------------+----------------+---------+------+-------+-----------------------------------------------------------+

使用不同的

0 个答案: