加入SQL Server表時顯示空值

Question

卡在此分配上，並且不顯示應有的空值。

說明：

列出每個部門處理的交易數量。 包括
沒有處理任何事務的部門。 按部門升序顯示結果。

這是我到目前為止的內容，它顯示具有事務的部門的總事務，並跳過空值。

SELECT 
    PC.Department, 
    COUNT(TD.TransactionID) AS TotalTransactions
FROM 
    TRANSACTION_DETAILS TD
INNER JOIN 
    PRODUCTS P ON P.ItemCode = TD.ItemCode
LEFT OUTER JOIN 
    PRODUCT_CATEGORIES PC ON P.Category = PC.Category
GROUP BY 
    PC.Department
ORDER BY 
    PC.Department ASC

Answer 1

SELECT      PC.Department, COUNT(TD.TransactionID) AS TotalTransactions
FROM        PRODUCT_CATEGORIES  PC 
LEFT JOIN   PRODUCTS            P   ON P.Category = PC.Category
LEFT JOIN   TRANSACTION_DETAILS TD  ON P.ItemCode = TD.ItemCode
GROUP BY    PC.Department
ORDER BY    PC.Department ASC

Answer 2

如果您還需要沒有價值的部門，則需要左加入開始PRODUCT_CATEGORIES（部門）

  SELECT PC.Department, COUNT(TD.TransactionID) AS TotalTransactions
  FROM PRODUCT_CATEGORIES PC
  LEFT  JOIN PRODUCTS P ON P.Category = PC.Category
  LEFT  JOIN TRANSACTION_DETAILS TD ON P.ItemCode = TD.ItemCode
  GROUP BY PC.Department
  ORDER BY PC.Department ASC