mysql查詢（根據他們的活動提取用戶數）

Question

我有2個MySQL表（用戶和評論） - 我想要做的是獲取一個報告，讓我有多少用戶作出1評論，有多少用戶作出2評論，有多少用戶發表了3條評論，有多少用戶發表了4條評論，按月份和年份分組。

我有這樣的查詢來獲取的，通過年度區分每個用戶提出的意見數量/月

select year(c.datecreated) as comment_year, month(c.datecreated) as comment_month,  
count(c.id) as num_comments 
from tblcomments c 
inner join tbluser u on u.id = c.userid 
where 
c.datecreated <= '2013-02-19' and c.datecreated >= '2012-03-01' 
group by c.userid, year(c.datecreated), month(c.datecreated) 

如何修改這個查詢給我我想要的結果嗎？

Answer 1

使用子查詢，以便將結果第二次：

SELECT ym, 
     SUM(c = 1) AS `num_1`, 
     SUM(c = 2) AS `num_2`, 
     SUM(c = 3) AS `num_3`, 
     SUM(c>= 4) AS `num_4+` 
FROM (
    SELECT DATE_FORMAT(datecreated, '%Y-%m') AS ym, COUNT(*) AS c 
    FROM  tblcomments 
    WHERE datecreated BETWEEN '2012-03-01' AND '2013-02-19' 
    GROUP BY ym, userid 
) t 
GROUP BY ym 

Answer 2

下面是做這件事 - 不知道你需要加入對tbluser，但我離開那裏：

SELECT comment_year, comment_month, 
    COUNT(userId) userCnt, 
    Num_Comments 
FROM (
    select 
    year(c.datecreated) as comment_year, 
    month(c.datecreated) as comment_month,  
    c.userid, 
    CASE WHEN count(c.id) >= 4 THEN '4+' ELSE CAST(COUNT(c.id) as varchar) END as num_comments 
    from tblcomments c 
    inner join tbluser u on u.id = c.userid 
    where 
    c.datecreated <= '2013-02-19' and c.datecreated >= '2012-03-01' 
    group by c.userid, year(c.datecreated), month(c.datecreated) 
) t 
GROUP BY comment_year, comment_month, Num_Comments; 

還有一些樣品小提琴：http://sqlfiddle.com/#!3/5fb5c/5