mysql查询(根据他们的事件获取用户数量)

Question

我有 2 个 MySQL 表(用户和评论)- 我想做的是获取一个报告，告诉我有多少用户发表了 1 条评论，有多少用户发表了 2 条评论，有多少用户发表了 3 条评论，还有多少用户发表了 4 条以上的评论，按月份和年份分组。

我有这个查询来获取每个用户按年/月分组的评论数

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)

如何修改此查询以获得我想要的结果？

Answer 1

再次使用子查询对结果进行分组:

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