Question

我在弄清楚如何编写此查询时遇到了很多麻烦。这是数据集的例子以及我需要查询的内容：

**System Table**    

SystemID   Active
1          T
2          T
3          T
4          F
5          F
6          F

**BlogPost Table**      

BlogPostID  SystemID    Create_Month
100         2           Jan
101         2           Jan
102         2           Feb
103         3           Feb
104         3           Mar
105         6           Mar
106         6           Mar

**Comment Table**       

Comment ID  BlogPostID  Liked
201         100         T
202         100         T
203         100         T
204         102         T
205         102         T
206         102         T
207         103         F

所以，总而言之，我试图得到：按月，向我展示在该月创建帖子的所有活动系统，他们在聚合中发布的帖子数量以及这些帖子子集的数量谁有评论就像。

最终结果如下：

Column 1 - Month

Column 2 - Count of Active Systems where a Post Created in Month

Column 3 - Count of Posts Applicable to those systems

Column 4 - Count of Applicable Posts that had comments that were liked

我甚至不知道从哪里开始。我的可怕“这显然是错误的”尝试在下面。非常感谢任何帮助，谢谢！

SELECT
  Month, 
  COUNT(DISTINCT system.systemid), 
  COUNT(blogpost.BlogPostID)
  COUNT(comments.commentiD)
FROM
  system INNER JOIN
  blogpost ON system.systemid = blogpost.systemid INNER JOIN
  comments ON blogpost.BlogPostID = comment.BlogPostID
WHERE
  system.active = T 
  AND comments.like = T
GROUP BY month

Answer 1

复杂的一个！

SELECT 
b.Create_Month, 
COUNT(DISTINCT s.SystemID) as SystemCount, 
COUNT(DISTINCT b.BlogPostID) as PostsCount,
COUNT(DISTINCT t.BlogPostID) as PostsWithLike

FROM System s 

JOIN BlogPost b 
ON s.systemID = b.systemID 
AND s.Active = 'T'  

LEFT JOIN Comment c 
ON b.BlogPostID = c.BlogPostID

LEFT JOIN
(
SELECT DISTINCT c.BlogPostID as BlogPostID
FROM 
Comment c 
GROUP BY c.BlogPostID 
HAVING SUM(if(c.Liked='T',1,0))>0
) as t
ON b.BlogPostID = t.BlogPostID

GROUP BY b.Create_Month

Answer 2

这可能是你想要的：

SELECT s.systemid, active, bp.create_month, bp.systemid, COUNT(bp.blogpostid), COUNT(c.liked)
FROM system AS s 
     LEFT OUTER JOIN Blogpost AS bp ON s.systemid = bp.systemid 
     LEFT OUTER JOIN Comment AS c ON bp.blogpostid = c.blogpostid 
WHERE active = 'T' AND c.Liked = 'T' GROUP BY s.systemid,bp.create_month

具有条件的许多INNER JOIN表中的多个计数

2 个答案: