mysql - 使用 LEFT JOIN 的 MYSQL 更新

Question

问题;

在下面的 MySQL 查询中，产生 ConnectionID 列表的内部查询返回 34 个 ConnectionID。然后当我将这两个查询作为更新一起运行时，查询结果表明只有 14 行受到影响。我对 UPDATE 函数的理解是否不正确？

笔记;

我正在尝试更新我的数据库，以便对于 Connections.PartnerID 等于 Partners.PartnerID 的任何给定连接，Partners 表中的 DefaultUserType 等于连接表中的 RoleID。

询问;

    UPDATE Connections
    LEFT JOIN Partners
        ON Connections.PartnerID = Partners.PartnerID
SET Connections.RoleID = Partners.DefaultUserType
WHERE
    ConnectionID IN(
        SELECT
            sub_qu_1.ConnectionID
        FROM
            (
                SELECT DISTINCT
                    Connections.ConnectionID,
                    Connections.MemberID,
                    Connections.FriendID,
                    Connections.RoleID,
                    Partners.DefaultUserType,
                    IF(Connections.RoleID = Partners.DefaultUserType,0,1)AS not_equal
                FROM
                    Connections
                LEFT JOIN Contacts ON Connections.FriendID = Contacts.EEID
                LEFT JOIN Partners ON Contacts.PartnerID = Partners.PartnerID
                WHERE
                    Partners.DefaultUserType NOT IN (28,29,30)
            )AS sub_qu_1
        WHERE
            not_equal = 1
        AND DefaultUserType IS NOT NULL
    )

Answer 1

我希望你没有几百万条记录！使用 Coalesce(val,0) 如果未在合作伙伴中记录，则设置为 0

    UPDATE Connections
SET Connections.RoleID = coalesce((select Partners.DefaultUserType FROM Partners WHERE Connections.PartnerID = Partners.PartnerID LIMIT 1),0)
WHERE
ConnectionID IN(
    SELECT
        sub_qu_1.ConnectionID
    FROM
        (
            SELECT DISTINCT
                Connections.ConnectionID,
                Connections.MemberID,
                Connections.FriendID,
                Connections.RoleID,
                Partners.DefaultUserType,
                IF(Connections.RoleID = Partners.DefaultUserType,0,1)AS not_equal
            FROM
                Connections
            LEFT JOIN Contacts ON Connections.FriendID = Contacts.EEID
            LEFT JOIN Partners ON Contacts.PartnerID = Partners.PartnerID
            WHERE
                Partners.DefaultUserType NOT IN (28,29,30)
        )AS sub_qu_1
    WHERE
        not_equal = 1
    AND DefaultUserType IS NOT NULL
)

已更正！