MySQL`INNER JOIN`同一表的倍數

是否可以通過INNER JOIN一個MySQL查詢來實現這個結果？MySQL`INNER JOIN`同一表的倍數

我有一個表與策略和表與會員。「策略」表包含與其成員表中的ID相對應的作者ID以及更新現有作者作品的作者ID。是否有可能同時獲得這兩個人的參考？像下面，不返回任何錯誤，但還沒有結果......

SELECT * FROM Strategies 
INNER JOIN Members AS a 
INNER JOIN Members AS b 
WHERE Strategies.ID='2' 
AND Strategies.AuthorID = a.ID 
AND Strategies.UpdateAuthorID = b.ID

來源

2013-03-05 SnareChops

使用LEFT JOIN：

SELECT 
    s.*, 
    a.Name AS MemberName, 
    b.Name AS UpdatedMemberName 
FROM Strategies AS s 
LEFT JOIN Members AS a ON s.AuthorID = a.ID AND s.ID = 2 
LEFT JOIN Members AS b ON s.UpdateAuthorID = b.ID AND s.ID = 2 ;

如果你希望他們在一列中使用COALESCE：

SELECT 
    s.*, 
    COALESCE(a.Name, b.Name) AS MemberName 
FROM Strategies AS s 
LEFT JOIN Members AS a ON s.AuthorID = a.ID AND s.ID = 2 
LEFT JOIN Members AS b ON s.UpdateAuthorID = b.ID AND s.ID = 2

來源

2013-03-05 06:59:34

我只需要將值賦給我的php變量，這樣我就可以顯示它們。所以最重要的應該是正確的？ – SnareChops 2013-03-05 07:01:23

@SnareChops兩者都可以正常工作，第一個會爲您提供兩列'AuthorId'，另一個列爲'UpdatedAuthorId'，但第二個查詢只會給您一列;不可空的。 – 2013-03-05 07:15:40

SELECT toD.dom_url AS ToURL, 
    fromD.dom_url AS FromUrl, 
    rvw.* 

FROM reviews AS rvw 

LEFT JOIN domain AS toD 
    ON toD.Dom_ID = rvw.rev_dom_for 

LEFT JOIN domain AS fromD 
    ON fromD.Dom_ID = rvw.rev_dom_from

如果域名是表名

來源

2013-03-05 06:59:49

MySQL`INNER JOIN`同一表的倍數

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