左連接 - >聚合函數問題

Question

我的數據庫中有四個不同的表：

線：

• thread_id單
• thread_content
• 時間戳

thread_rating：

• thread_rating_id
• thread_id單
• 喜歡
• 不喜歡的

thread_report：

• thread_report_id
• thread_id單

thread_impression：

• thread_impression_id
• thread_id單

我將使用此SQL-Query加入這些表

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應該返回所有thread_id，其中包含計算出的喜歡和不喜歡的內容，以百分比表示的喜歡，時間戳，線程插入數據庫的時間以及報告的百分比（展示次數，時間，線程都顯示給用戶）。 ..

幾乎所有結果都是正確的，唯一不合適的結果是喜歡和不喜歡。

如果我在查詢前面加上一個count（*），我可以看到，正確的結果計數為1，錯誤的結果有時計數最多為60.看起來有交叉連接問題.. 。

我認為這是分組的問題，或者我應該接受聯接。

我見過帶有子選擇的解決方案。 但我認為這不是解決這個問題的好方法......

我在這做錯了什么？

Answer 1

tra表每個thread_id有多個記錄。 這導致SUM函數中的雙重計數。
在子選擇中進行求和，按連接字段分組。
這樣，你只需要在tra2有一個thread_id加入，並避免重復行。

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