每周多列计数答案

【问题标题】：Multiple column counts by week每周多列计数
【发布时间】：2012-12-06 14:58:31
【问题描述】：

我有以下两张表：

帖子

post_id
post_title
post_timestamp

comment_id
posts_post_id
comment_content
comment_timestamp

我想创建一个显示每周发帖数和评论数的报告。像这样的：

Week    StartDate      Posts     Comments
1       1/1/2012       100        305
2       1/8/2012       115        412

我有这个查询，但它只从 Posts 表中提取。

select makedate( left(yearweek(p.post_timestamp),1),week(p.post_timestamp, 2 ) * 7 ) as Week, COUNT(p.post_id) as Posts  
FROM cl_posts p
GROUP BY Week
ORDER BY WEEK(p.post_timestamp)

如何添加评论计数？

【问题讨论】：

标签： mysql sql

【解决方案1】：

我认为你需要这样的东西：

select
  week(post_timestamp) as Week,
  adddate(date(post_timestamp), INTERVAL 1-DAYOFWEEK(post_timestamp) DAY) as StartDate,
  count(distinct post_id),
  count(comment_id)
from
  posts left join comments
  on comments.posts_post_id = posts.post_id
group by Week, StartDate

【讨论】：

干净简单。像魅力一样工作！

【解决方案2】：

这是一种方法，使用join：

select coalesce(p.week, c.week) as week, p.Posts, c.Comments
from (select makedate( left(yearweek(p.post_timestamp),1),week(p.post_timestamp, 2 ) * 7 ) as Week,   
             COUNT(*) as Posts  
      FROM cl_posts p
      GROUP BY Week
     ) p full outer join
     (select makedate( left(yearweek(c.comment_timestamp),1),week(c.comment_timestamp, 2 ) * 7 ) as Week,   
             COUNT(*) as Comments
      FROM cl_comments c
      GROUP BY Week
     ) c
     on p.week = c.week
order by 1

我使用 full outer join 而不是另一种连接类型的原因是即使其中一个或其他计数为 0 也能保持数周。我没有将表连接在一起的原因大概是因为您想要评论日期的报告，而不是与评论相关的帖子的发布日期。

【讨论】：

我对 COALESCE 和 SUB-QUERIES 的工作不多，所以我想试试你的查询。但是，查询没有正确计算 cmets。知道为什么吗？此外，MySQL 不支持 FULL OUTER JOINS。
是的。我使用 post_timestamp 而不是 comment_timestamp 来表达你一周的部分表达。