MySQL内部连接与同一张表的条件

Question

我有一个名为activities 的表，其中包括不同类型的活动，其中一些是相关的。 A 类型的每个活动都与B 类型的活动匹配，为简单起见，我们假设没有丢失数据。到目前为止，设置与this question 非常相似。

每个活动都有几列，包括activity_type、related_activity_id 和location_id。我可以很容易地查询这些对：

SELECT 
A.location_id as 'A location id',
B.location_id as 'B location id'
FROM (SELECT * FROM activities WHERE `activities`.`activity_type` IN ('Activities::A') AND (`activities`.`related_activity_id` IS NOT NULL)) AS A
INNER JOIN (SELECT * FROM activities WHERE `activities`.`activity_type` IN ('Activities::B') AND (`activities`.`related_activity_id` IS NOT NULL)) AS B
ON A.related_act_id = B.id;

问题是当我想找到不匹配的对时，即A的位置与B的位置不匹配的对。我尝试过使用

WHERE A_location_id <> B_location_id

但它无法识别列：

错误代码：1054。“where”中的未知列“A_location_id” 子句' 0.734 秒

我不情愿地将where子句转换为：

WHERE A.location_id <> B.location_id

但是现在查询非常长，并且 MySQL 工作台窒息，最终杀死了查询：

错误代码：2013。在查询期间丢失与 MySQL 服务器的连接

我尝试过使用更长的超时查询，但它没有一点帮助。关于如何解决这个问题的任何想法？

Answer 1

对我来说不是很清楚，但也许你可以这样尝试

SELECT 
A.location_id as 'A location id',
B.location_id as 'B location id'
FROM activities c
INNER JOIN activities parent ON parent.activity_type = c.activity_type
WHERE related_activity_id IS NOT NULL AND c.location_id != p.location_id

Answer 2

你可以在 MySQL 中使用 HAVING

BUT SELECT * is bad From 因为你不需要所有列

    SELECT 
        A.location_id AS 'A location id',
        B.location_id AS 'B location id'
    FROM
        (SELECT 
            *
        FROM
            activities
        WHERE
            `activities`.`activity_type` IN ('Activities::A')
                AND (`activities`.`related_activity_id` IS NOT NULL)) AS A
            INNER JOIN
        (SELECT 
            *
        FROM
            activities
        WHERE
            `activities`.`activity_type` IN ('Activities::B')
                AND (`activities`.`related_activity_id` IS NOT NULL)) AS B ON A.related_activity_id= B.id
    HAVING A_location_id <> B_location_id;

所以我会将查询减少到，MySQL 必须处理更少的数据

SELECT 
    A.location_id AS 'A location id',
    B.location_id AS 'B location id'
FROM
    (SELECT 
        location_id,
        related_activity_id
    FROM
        activities
    WHERE
        `activities`.`activity_type` IN ('Activities::A')
            AND (`activities`.`related_activity_id` IS NOT NULL)) AS A
        INNER JOIN
    (SELECT 
        location_id,
        id
    FROM
        activities
    WHERE
        `activities`.`activity_type` IN ('Activities::B')
            AND (`activities`.`related_activity_id` IS NOT NULL)) AS B ON A.related_activity_id = B.id
HAVING A_location_id <> B_location_id;

最后如果查询仍然需要很长时间增加wait_timeout