我很好奇，爲什麼這些結果是不同的

Question

我開始了與一個粗略的草稿查詢：

SELECT S.Type, 
COUNT(DISTINCT C.StateProvince) 
FROM INV_LINE_ITEM ILI JOIN STOVE S ON ILI.FK_StoveNbr = S.SerialNumber 
JOIN INVOICE I ON I.InvoiceNbr = ILI.FK_InvoiceNbr 
JOIN CUSTOMER C ON I.FK_CustomerID = C.CustomerID 
WHERE C.Country = 'USA' 
AND S.Type IN (SELECT S.Type 
FROM INV_LINE_ITEM ILI JOIN STOVE S ON ILI.FK_StoveNbr = S.SerialNumber 
JOIN INVOICE I ON I.InvoiceNbr = ILI.FK_InvoiceNbr 
JOIN CUSTOMER C ON I.FK_CustomerID = C.CustomerID 
WHERE C.Country = 'CAN') 
GROUP BY S.Type; 

它返回的結果如下：

Type    
--------------- ----------- 
FiredAlways  9 
FiredNow  8 

所以，一旦我得到了查詢以我想要的方式工作，我決定對它進行一些格式化，並且我注意到一些奇怪的東西。

這個查詢會產生上述結果：

SELECT 
CAST(S.Type as CHAR (10)) AS 'Stove Type', 
COUNT(DISTINCT C.StateProvince) AS 'Number of Sales' 
FROM STOVE S, INV_LINE_ITEM ILI, INVOICE I, CUSTOMER C 
WHERE S.SerialNumber = ILI.FK_StoveNbr 
AND ILI.FK_InvoiceNbr = I.InvoiceNbr 
AND I.FK_CustomerID = C.CustomerID 
AND C.Country = 'USA' 
AND S.Type IN 
(SELECT S.Type 
FROM STOVE S, INV_LINE_ITEM ILI, INVOICE I, CUSTOMER C 
WHERE S.SerialNumber = ILI.FK_StoveNbr 
AND ILI.FK_InvoiceNbr = I.InvoiceNbr 
AND I.FK_CustomerID = C.CustomerID 
AND C.Country = 'CAN') 
GROUP BY S.Type; 

但此查詢不：

SELECT 
CAST(S.Type as CHAR (10)) AS 'Stove Type', 
COUNT(DISTINCT C.StateProvince) AS 'Number of Sales' 
FROM STOVE S, INV_LINE_ITEM ILI, INVOICE I, CUSTOMER C 
WHERE S.SerialNumber = ILI.FK_StoveNbr 
AND ILI.FK_InvoiceNbr = I.InvoiceNbr 
AND I.FK_CustomerID = C.CustomerID 
AND C.Country = 'USA' 
AND S.Type IN 
(SELECT CAST(S.Type as CHAR (10)) 
FROM STOVE S, INV_LINE_ITEM ILI, INVOICE I, CUSTOMER C 
WHERE S.SerialNumber = ILI.FK_StoveNbr 
AND ILI.FK_InvoiceNbr = I.InvoiceNbr 
AND I.FK_CustomerID = C.CustomerID 
AND C.Country = 'CAN') 
GROUP BY S.Type; 

相反，它會產生這樣的：

Stove Type Number of Sales 
---------- --------------- 
FiredNow 8 

而且我不真的確定爲什麼。我原以爲我只編輯第10行的S.Type以匹配第2行的S.Type，但很明顯發生了更多事情。

Answer 1

因爲「FiredAlways」超過了要投射的10個角色。