MySQL查询将第一次连接限制为特定行数

Question

我正在尝试运行一个连接3个表的查询，我想将第一个连接限制为仅5行。最终结果可以返回任意数量的行，因此我不想将LIMIT添加到查询的末尾。

这是我的查询，它有效，但显然不会将第一次连接限制为5行。我尝试过一个子查询，我相信这是完成此任务的唯一方法，我尝试的一切都会出错。我似乎无法应用我见过的例子，我的情况。

SELECT mw_customer.customer_id, mw_customer.customer_uid, mw_campaign.customer_id, mw_campaign.campaign_id, mw_campaign.type, mw_campaign.status, mw_campaign_delivery_log.campaign_id, mw_campaign_delivery_log.subscriber_id
   FROM mw_customer 
   JOIN mw_campaign
        ON mw_customer.customer_id = mw_campaign.customer_id
        AND mw_customer.customer_uid = 'XYZ'
        AND mw_campaign.type = 'regular'
        AND mw_campaign.status = 'sent'
   JOIN mw_campaign_delivery_log
        ON mw_campaign.campaign_id = mw_campaign_delivery_log.campaign_id

所以我想要做的是将“JOIN mw_customer”限制为最多5行，然后在JOIN mw_campaign_delivery_log之后，可以有任意数量的行。

由于

Answer 1

使用LIMIT 5在子查询中包装第一个连接。

SELECT t.customer_id, t.customer_uid, t.campaign_id, t.type, t.status, l.subscriber_id
   FROM (SELECT cus.customer_id, cus.customer_uid, cam.campaign_id, cam.type, cam.status
         FROM mw_customer AS cus
         JOIN mw_campaign AS cam
            ON cus.customer_id = cam.customer_id
         WHERE cus.customer_uid = 'XYZ'
            AND cam.type = 'regular'
            AND cam.status = 'sent'
         LIMIT 5) AS t
   JOIN mw_campaign_delivery_log AS l
        ON t.campaign_id = l.campaign_id

请注意，LIMIT没有ORDER BY意味着所选的5行将无法预测。