SQL帮助内连接左连接

Question

我的查询是：

SELECT Pics.ID, Pics.ProfileID, Pics.Position, Rate.ID as RateID, Rate.Rating, Rate.ProfileID, Gender
FROM Pics
    INNER JOIN Profiles ON Pics.ProfileID = Profiles.ID
    LEFT JOIN Rate ON Pics.ID = Rate.PicID
WHERE Gender = 'female'
ORDER BY Pics.ID

结果是：

ID ProfileID Position RateID Rating ProfileID Gender
23 24        1        59     9      42        female
24 24        2        33     8      32        female
23 24        1        53     3      40        female
26 24        4        31     8      32        female
30 25        4        30     8      32        female
24 24        2        58     4      42        female

现在，我要执行另一个查询，即：如果Rate.ProfileID = 32，则删除任何包含相同Pics.ID的行。

所以留下：

ID ProfileID Position RateID Rating ProfileID Gender
23 24        1        59     9      42        female
23 24        1        53     3      40        female

并删除所有重复的Pics.ID，因此它们都是23，因此只保留了上述之一：

23 24 1 59 9 42母头或23 24 1 53 3 40母头

Answer 1

您可能应该摆脱“神奇数字”，例如32。也就是说，我认为这将为您提供所需的东西。

SELECT
    P.ID,
    P.ProfileID,
    P.Position,
    R.ID as RateID,
    R.Rating,
    R.ProfileID,
    PR.Gender
FROM
    Pics P
INNER JOIN Profiles PR ON PR.ID = P.ProfileID
LEFT JOIN Rate R ON R.PicID = P.ID
WHERE
    PR.Gender = 'female' AND
    NOT EXISTS (
        SELECT *
        FROM Pics P2
        INNER JOIN Profiles PR2 ON PR2.ID = P2.ProfileID
        INNER JOIN Rate R2 ON R2.PicID = P2.ID AND R2.ProfileID = 32
        WHERE
            P2.ID = P.ID
    )
ORDER BY
    P.ID

Answer 2

@Shadow因为第二行包含Rate.ProfileID = 32，并且该Pic.ID = 24，所以它必须删除所有Pic.ID = 24，这也删除了底行。

SELECT Pics.ID, Pics.ProfileID, Pics.Position, Rate.ID as RateID, Rate.Rating, Rate.ProfileID, Gender
FROM Pics
INNER JOIN Profiles ON Pics.ProfileID = Profiles.ID
LEFT JOIN Rate ON Pics.ID = Rate.PicID
WHERE Gender = 'female' AND Pics.ID NOT IN (
    SELECT Pics.ID 
    FROM Pics
    INNER JOIN Profiles ON Pics.ProfileID = Profiles.ID
    LEFT JOIN Rate ON Pics.ID = Rate.PicID
    WHERE Gender = 'female' AND Rate.ProfileID = 32)

ORDER BY Pics.ID

Answer 3

尝试这个：

SELECT Pics.ID, Pics.ProfileID, Pics.Position, Rate.ID as RateID, 
       Rate.Rating, Rate.ProfileID, Gender
FROM Pics
INNER JOIN Profiles ON Pics.ProfileID = Profiles.ID
LEFT JOIN Rate ON Pics.ID = Rate.PicID
LEFT JOIN Rate AS r 
   ON Rate.ProfileID = r.ProfileID AND Rate.ID > r.ID
WHERE Gender = 'female' AND (Pics.ProfileID <> 32) AND (r.ID IS NULL)
ORDER BY Pics.ID

最后一个LEFT JOIN操作使用ON子句中的此谓词帮助识别重复项：

Rate.ProfileID = r.ProfileID

如果存在此类重复项（如Rate.ProfileID = 42的情况），则由于以下条件，仅返回具有最大 Rate.ID ：

Rate.ID > r.ID (`ON` clause)

和

(r.ID IS NULL) (`WHERE` clause)