SQL從選擇

Question

伊夫刪除特定的行了一個表：

UserA UserB UserBB UserAA 

例如：

1 2 2 1 
1 3 3 1 
2 1 1 2 
2 4 4 2 
2 5 5 2 
5 2 2 5 

我想實現的是刪除行（重複），如僅讓行作爲例如：

1 2 2 1 
1 3 3 1 
2 4 4 2 
2 5 5 2 



2 1 1 2 -> deleted because there is already 1 2 2 1 
5 2 2 5 -> deleted because there is already 2 5 5 2 

如何編寫這樣的查詢？

感謝您的幫助

Answer 1

- 查找重複的行

SELECT MAX(ID) as ID, CustName, Pincode FROM #Customers 
GROUP BY CustName, Pincode 
HAVING COUNT(*) > 1 

- 刪除重複的行

DELETE FROM #Customers 
WHERE ID IN 
(SELECT MAX(ID) FROM #Customers 
GROUP BY CustName, Pincode 
HAVING COUNT(*) > 1) 

從MSDN服用。 ： http://archive.msdn.microsoft.com/SQLExamples/Wiki/View.aspx?title=DuplicateRows

讓我知道你是否無法從該代碼中找出它。

這可能會更接近您的需求。 ：

DELETE FROM TABLE 
WHERE USERA IN (SELECT MAX(USERA) FROM TABLE 
GROUP BY USERA, USERB, USERBB, USERAA HAVING COUNT(*) > 1) 

Answer 2

下面還介紹了UserA和UserB在兩行之間相等但UserAA和UserBB切換相反的情況。你的問題有點不清楚究竟是什麼構成重複。但希望這至少能指出你在正確的方向。

我會首先將它變成SELECT聲明，並確保它返回您認爲應該刪除的行並僅返回那些行。

DELETE T1 
FROM 
    My_Table T1 
INNER JOIN My_Table T2 ON 
    (
     T2.UserA = T1.UserA AND 
     T2.UserB = T1.UserB AND 
     T2.UserAA = T1.UserBB AND 
     T2.UserBB = T1.UserAA AND 
     T2.UserAA < T2.UserBB 
    ) OR 
    (
     T2.UserA = T1.UserB AND 
     T2.UserB = T1.UserA AND 
     T2.UserAA = T1.UserAA AND 
     T2.UserBB = T1.UserBB AND 
     T2.UserA < T2.UserB 
    ) OR 
    (
     T2.UserA = T1.UserB AND 
     T2.UserB = T1.UserA AND 
     T2.UserAA = T1.UserBB AND 
     T2.UserBB = T1.UserAA AND 
     T2.UserA < T2.UserB 
    ) 

Answer 3

這足以只是補充：

當用戶A <用戶B