自我加入不同的表

Question

我写了以下查询：

SELECT R1.RELATIONSHIP_ID, R1.SUPPLIER_ACCOUNT_ID, R2.BUYER_ACCOUNT_ID
FROM RELATIONSHIP R1 JOIN RELATIONSHIP R2
ON (R1.RELATIONSHIP_ID = R2.RELATIONSHIP_ID)
ORDER BY SUPPLIER_ACCOUNT_ID;

表格：
1. RELATIONSHIP：列：RELATIONSHIP_ID, SUPPLIER_ACCOUNT_ID, BUYER_ACCOUNT_ID ...
2. ACCOUNT：ACCOUNT_ID, XX_ACCOUNT_ID ....

并且到目前为止正确地给出了结果

但是，我想要的更复杂。我需要使用列called XX_ACOUNT_ID替换第二列和第三列，以显示两次。每个SUPPLIER_ACCOUNT_ID和BUYER_ACCOUNT_ID都有唯一的XX_ACCOUNT_ID和唯一的ACCOUNT_ID。 XX_ACCOUNT_ID属于表ACCOUNTS，其中ACCOUNT_ID（此列引用了​​SUUPLIER_ACCOUNT_ID & BUYER_ACCONT_ID）和XX_ACCOUNT_ID。我有点困惑，它需要嵌套的自联接还是多个内部联接？或子查询来解决这个问题？

Answer 1

如果引用的表中始终存在R1.Supplier_Account_ID和R2.Buyer_Account_ID，则多个内部联接应该起作用。尝试这样的事情：

SELECT R1.RELATIONSHIP_ID, AcctSupp.XX_ACOUNT_ID, AcctBuyer.XX_ACOUNT_ID
FROM RELATIONSHIP R1
JOIN RELATIONSHIP R2 ON (R1.RELATIONSHIP_ID = R2.RELATIONSHIP_ID)
JOIN Accounts AcctSupp ON R1.SUPPLIER_ACCOUNT_ID = AcctSupp.Account_ID
JOIN Accounts AcctBuyer ON R2.BUYER_ACCOUNT_ID = AcctBuyer.Account_ID
ORDER BY SUPPLIER_ACCOUNT_ID;

如果引用的表中不存在值，则使用左连接：

SELECT R1.RELATIONSHIP_ID, AcctSupp.XX_ACOUNT_ID, AcctBuyer.XX_ACOUNT_ID
FROM RELATIONSHIP R1
JOIN RELATIONSHIP R2 ON (R1.RELATIONSHIP_ID = R2.RELATIONSHIP_ID)
LEFT JOIN Accounts AcctSupp ON R1.SUPPLIER_ACCOUNT_ID = AcctSupp.Account_ID
LEFT JOIN Accounts AcctBuyer ON R2.BUYER_ACCOUNT_ID = AcctBuyer.Account_ID
ORDER BY SUPPLIER_ACCOUNT_ID;

Answer 2

也许我误解了这个问题，但我不明白为什么你需要自我加入：

SELECT R.Relationship_Id,
    Supplier.xx_account_id sup_id,
    Buyer.xx._account_id buy_id
FROM Relationship AS R
JOIN Accounts AS Buyer
    ON R.Buyer_account_Id = Buyer.Account_Id
JOIN Accounts AS Supplier
    ON R.Supplier_account_Id = Supplier.Account_Id