MySql：查询以根据日期添加和分类不同的数据

Question

我正在尝试提取每个唯一用户每月发布的“帖子”总数，并将其分类为 2-3 个帖子和 4 个以上帖子。请看下面的例子。无法正常工作，请帮忙。

示例数据库：

id         Date                    ID             Posts     otherData
-----      ------                  -------        ------    -----------
1          2015-01-24 14:13:50     user1           1        2
2          2015-01-24 14:13:50     user1           3        1
3          2015-01-24 14:13:50     user2           2        4
4          2015-01-24 14:13:50     user3           7        3
5          2015-01-24 14:13:50     user4           0        2
6          2015-02-24 04:13:50     user1           1        3
7          2015-02-24 04:13:50     user1           1        1
8          2015-02-24 04:13:50     user3           1        2

预期结果：

Month     totalUsersThatHavePosted    1 post     2-3Posts          4+Posts
-----     -------------------------   ------     ---------         ------- 
12015     3                           0          1                 2
22015     2                           1          1                 0

我正在尝试这样的查询（但不要认为我很接近）：

SELECT CONCAT( MONTH(  `Date` ) , YEAR(  `Date` ) ) AS Month, COUNT(DISTINCT `ID`) 
FROM  `myDB` 
WHERE  `Posts` >0
GROUP BY CONCAT( MONTH(  `Date` ) , YEAR(  `Date` ) ) 

Answer 1

我相信这会给你想要的：

SELECT 
Month,COUNT(DISTINCT(user_total)) AS totalUsersThatHavePosted,
SUM((user_total) = 1) as 1_post,
SUM((user_total) in (2, 3)) as 2_3_posts, 
SUM((user_total) > (3)) as 4_plus_posts 
FROM 
(
    SELECT CONCAT(MONTH(Date),
    YEAR(Date)) AS Month,
    ID,
    SUM(Posts) AS user_total 
    FROM myDB 
    WHERE Posts > 0
    GROUP BY Date,ID
) 
AS desired_subset 

GROUP BY Month;

Answer 2

这是一个双重聚合查询。首先，按用户和月份聚合，得到计数。然后按月汇总以进行最终计数：

select yr, mon, count(*) as TotalUsersPosted,
       sum(cnt in (2, 3)) as posts_2_3,
       sum(cnt >= 4) as posts_4pl 
from (select id, year(date) as yr, month(date) as mon, count(*) as cnt
      from mydb
      group by id, year(date), month(date)
     ) t
group by yr, mon