左连接 - >聚合函数问题

Question

我的数据库中有四个不同的表：

线：

• thread_id单
• thread_content
• 时间戳

thread_rating：

• thread_rating_id
• thread_id单
• 喜欢
• 不喜欢的

thread_report：

• thread_report_id
• thread_id单

thread_impression：

• thread_impression_id
• thread_id单

我将使用此SQL-Query加入这些表

SELECT t.thread_id,
t.thread_content,
SUM(tra.liked) AS liked,
SUM(tra.disliked) AS disliked,
t.timestamp,
((100*(tra.liked + SUM(tra.liked))) / (tra.liked + SUM(tra.liked) + (tra.disliked + SUM(tra.disliked)))) AS liked_percent,
((100*(COUNT(DISTINCT tre.thread_report_id)) / ((COUNT(DISTINCT ti.thread_impression_id))))) AS reported_percent
FROM thread AS t
LEFT JOIN thread_rating AS tra ON t.thread_id = tra.thread_id
LEFT JOIN thread_report AS tre ON tra.thread_id = tre.thread_id
LEFT JOIN thread_impression AS ti ON tre.thread_id = ti.thread_id
GROUP BY t.thread_id
ORDER BY liked_percent

Query应该返回所有thread_id，其中包含计算出的喜欢和不喜欢的内容，以百分比表示的喜欢，时间戳，线程插入数据库的时间以及报告的百分比（展示次数，时间，线程都显示给用户）。 ..

几乎所有结果都是正确的，唯一不合适的结果是喜欢和不喜欢。

如果我在查询前面加上一个count（*），我可以看到，正确的结果计数为1，错误的结果有时计数最多为60.看起来有交叉连接问题.. 。

我认为这是分组的问题，或者我应该接受联接。

我见过带有子选择的解决方案。 但我认为这不是解决这个问题的好方法......

我在这做错了什么？

Answer 1

tra表每个thread_id有多个记录。 这导致SUM函数中的双重计数。
在子选择中进行求和，按连接字段分组。
这样，你只需要在tra2有一个thread_id加入，并避免重复行。

SELECT t.thread_id,
  t.thread_content,
  tra2.liked
  tra2.disliked,
  t.timestamp,
  tra2.liked_percent,
  ((100*(COUNT(DISTINCT tre.thread_report_id)) / ((COUNT(DISTINCT ti.thread_impression_id))))) AS reported_percent
FROM thread AS t
LEFT JOIN (
     SELECT 
       tra.thread_id 
       , SUM(tra.liked) AS liked
       , SUM(tra.disliked) AS disliked
       , ((100*(tra.liked + SUM(tra.liked))) / (tra.liked + SUM(tra.liked) + (tra.disliked + SUM(tra.disliked)))) AS liked_percent 
     FROM thread_rating AS tra
     GROUP BY tra.thread_id
) as tra2 ON t.thread_id = tra2.thread_id
LEFT JOIN thread_report AS tre ON tra.thread_id = tre.thread_id
LEFT JOIN thread_impression AS ti ON tre.thread_id = ti.thread_id
GROUP BY t.thread_id
ORDER BY liked_percent DESC