子查詢不輸出正確的結果？

Question

我希望有人能幫助我解決這個問題，我一直在嘗試不同的組合，但似乎無法得到正確的結果。

首先，我有3個表，類別，部門和主人，主人有FK。我想得到每個部門的總時間總和和部門類別總時間總和，以便我可以看到哪個部門有多少時間用於該類別，都應該按部門分組並且按正確的順序？

我可以得到結果，但不出來吧，這裏是我的代碼...

SELECT a.department, time_spent , COUNT(DISTINCT (a.department)), sum_quarantine FROM 

    (SELECT d.department, SUM(time_spent) as time_spent 
    FROM master as m 
    INNER JOIN department as d ON d.dept_id = m.dept_id GROUP BY d.department) AS a, 

    (SELECT d.department, c.category, SUM(time_spent) as sum_quarantine 
    FROM master as m 
    INNER JOIN category as c ON c.cat_id = m.cat_id 
    INNER JOIN department as d ON d.dept_id = m.dept_id 
    WHERE category = 'Quarantine' GROUP BY d.department) as b 

    GROUP BY b.department 

Answer 1

你想要可以不子查詢來完成，利用一個CASE WHEN的在SUM，所以什麼它只是概括你所感興趣的東西（「隔離」）：

SELECT  d.department, 
      SUM(CASE c.category 
       WHEN 'Quarantine' THEN time_spent 
       END) as sum_quarantine, 
      SUM(time_spent) time_spent, 
      COUNT(DISTINCT (c.category)) category_count 
FROM  master as m 
INNER JOIN category as c ON c.cat_id = m.cat_id 
INNER JOIN department as d ON d.dept_id = m.dept_id 
GROUP BY d.department 
ORDER BY 1 

這裏是fiddle。

請注意，我還添加了一個計數，因爲您的嘗試中有一個。但你的總是會返回1，所以我不知道你在找什麼。我已經添加了與部門相關的類別數量。

此外，您並未指定所需的訂單，但很容易修改ORDER BY條款。上面的查詢結果排序按部門，但舉例來說如果你想通過第二列按降序排序，然後做：

... 
ORDER BY 2 DESC 

如果結果包括NULL值，你希望有個零，而不是，然後使用COALESCE函數。例如：

COALESCE(SUM(time_spent), 0) time_spent,