可空主鍵

Question

我有兩個表。

採購：

• PurchaseId
• SenderId
• ReceiverId

客戶：

• Customerid（小學唯一的）
• CUSID（不初級不是唯一的，不允許使用NULL）
• FirsName
• LastName

我要讓所有購買用戶名和lastnames在客戶表中的一些報道。 我不能做任何關係。所有我的代碼給我錯誤或返回錯誤的結果。 請幫助我（接收者和發送者的值在客戶表中是相同的CUSID） 關係錯誤：因爲我的字段不允許爲空，所以我無法創建任何主鍵。

(select (tbl_Customers.FirstName + '-' + tbl_Customers.LastName) as receiver 
FROM   tbl_PurchaseForms 
INNER JOIN 
tbl_Customers ON tbl_PurchaseForms.ReceiverUId = tbl_Customers.CUSID) 
or 
(select (tbl_Customers.FirstName + '-' + tbl_Customers.LastName) as sender 
FROM   tbl_PurchaseForms 
INNER JOIN 
tbl_Customers ON tbl_PurchaseForms.SenderUId = tbl_Customers.CUSID) 

Answer 1

我對你的問題誠然有點困惑，但它聽起來像你試圖返回所有誰接收或發送的東西從你的購買表格，鏈接對你cusid領域的客戶？

如果是這樣，這樣的事情應該工作（我已經包括所謂的購買類型，如果你需要發送者和接收者之間區分一個額外的列）：

SELECT 
    'Sender' as PurchaseType, 
    C.FirstName, 
    C.LastName 
FROM Customers C 
    JOIN Purchase P ON C.CUSID = P.SenderId 
UNION 
SELECT 
    'Receiver' as PurchaseType, 
    C.FirstName, 
    C.LastName 
FROM Customers C 
    JOIN Purchase P ON C.CUSID = P.ReceiverId 

好運。

Answer 2

Select p.* 
,(Select c.FirstName + '-' + c.LastName from customers c where c.CUSID = P.ReceiverId) as receiver 
,(Select c.FirstName + '-' + c.LastName from customers c where c.CUSID = P.SenderId) as Sender 
from purchase p 

而購買的設計應啓用此

Select p.* 
,(Select c.FirstName + '-' + c.LastName from customers c where c.Customerid = P.ReceiverId) as receiver 
,(Select c.FirstName + '-' + c.LastName from customers c where c.Customerid = P.SenderId) as Sender 
from purchase p