[英]Merge two rows that contain the same Id but different data into one row
我對大家有一個非常棘手的問題
假設我有下表
表AccountType :
Id Type
1 Checking
2 Savings
表Customer_Account :
Customer_Id Account_Type_Id
450 1
450 2
451 1
表Customer_Account包含客戶ID和其帳戶類型ID的列表。 Account_Type_Id是來自AccountType.Id的外鍵。
假設在Customer_Account表中,名為Josh(id 450)的客戶可以同時具有支票帳戶和儲蓄帳戶,如上所示。 我可以通過在AccountType表上兩次進行一次LEFT JOIN來輸出此客戶及其ID和帳戶類型:
SELECT CustAccount.Customer_Id AS Id, Account1.Type AS Account_Type_1, Account2.Type AS Account_Type_2
FROM Customer_Account CustAccount
LEFT JOIN AccountType Account1
ON Account1.Id = CustAccount.Account_Type_Id
LEFT JOIN AccountType Account2
ON Account2.Id = CustAccount.Account_Type_Id
輸出將是:
Id Account_Type_1 Account_Type_2
450 Checking Checking
450 Savings Savings
451 Checking Checking
我要嘗試做的是,如果像Josh(id 450)這樣的客戶同時擁有支票賬戶和儲蓄賬戶,我想將上述兩行數據輸出為一行,如下所示:
Id Account_Type_1 Account_Type_2
450 Checking Savings
而且,如果客戶只有一種類型的帳戶(例如此處的ID為451的客戶),我只希望該類型的帳戶出現在相應的列下,如下所示:
Id Account_Type_1 Account_Type_2
451 Checking
或者,如果ID為451的客戶只有一個儲蓄帳戶,則輸出應為:
Id Account_Type_1 Account_Type_2
451 Savings
我希望“檢查”僅顯示在Accoun_Type_1下,而“儲蓄”顯示在Account_Type_2下。 如果我執行GROUP BY CustAccount.Customer_Id,則會得到以下信息:
Id Account_Type_1 Account_Type_2
450 Checking Checking
451 Checking Checking
任何專家的幫助將不勝感激。
謝謝。
這看起來像是FULL OUTER JOIN的簡單應用程序:
SELECT COALESCE(ac1.id, ac2.id) AS id, ac1.Account_Type_1, ac2.Account_Type_2
FROM (SELECT c.Customer_ID AS Id, t.Type AS Account_Type_1
FROM Customer_Account AS c
JOIN AccountType AS t ON c.Account_Type_ID = t.ID AND t.ID = 1) AS ac1
FULL OUTER JOIN
(SELECT c.Customer_ID AS Id, t.Type AS Account_Type_2
FROM Customer_Account AS c
JOIN AccountType AS t ON c.Account_Type_ID = t.ID AND t.ID = 2) AS ac2
ON ac1.Id = ac2.Id;
如果您的DBMS不支持FULL OUTER JOIN但支持LEFT OUTER JOIN,則可以使用:
SELECT ac0.id, ac1.Account_Type_1, ac2.Account_Type_2
FROM (SELECT DISTINCT c.Customer_ID AS Id FROM Customer_Account AS c) AS ac0
LEFT OUTER JOIN
(SELECT c.Customer_ID AS Id, t.Type AS Account_Type_1
FROM Customer_Account AS c
JOIN AccountType AS t ON c.Account_Type_ID = t.ID AND t.ID = 1) AS ac1
ON ac0.id = ac1.id
LEFT OUTER JOIN
(SELECT c.Customer_ID AS Id, t.Type AS Account_Type_2
FROM Customer_Account AS c
JOIN AccountType AS t ON c.Account_Type_ID = t.ID AND t.ID = 2) AS ac2
ON ac0.Id = ac2.Id;
第一個子查詢生成存在的客戶ID列表; 第二個生成帳戶類型1(檢查)的列表; 第三個生成帳戶類型2(保存)的列表。 聯接可確保正確識別每個帳戶。
為您的ON子句添加更多條件:
ON Account1.Id = CustAccount.Account_Type_Id and Account1.Account_Type_Id = 1
ON Account2.Id = CustAccount.Account_Type_Id and Account2.Account_Type_Id = 2
將導致輸出包括客戶持有的帳戶。 如果他們只有一個帳戶,則另一帳戶類型將為NULL。
編輯:對不起,我沒有意識到您沒有客戶表。 您可以使用不同的Customer_Id值列表創建一個臨時表,並將其用作JOIN中的第一個表。
select distinct Customer_Id into #Customers
from Customer_Account
或者更簡單:
select distinct C.Customer_Id,
( select 'Checking' from Customer_Account where Customer_Id = C.CustomerId and Account_type_Id = 1 ) as Account_Type_1,
( select 'Savings' from Customer_Account where Customer_Id = C.CustomerId and Account_type_Id = 2 ) as Account_Type_2,
from Customer_Account as C
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