Mysql更新和连接查询

Question

我在使用 Sum 更新查询时遇到问题。我有两张 table 进行事件和捐款。我想更新特定事件的每笔捐款总额

tb_campaign

1. 编号
2. 姓名
3. 总捐款

tb_捐赠

1. 编号
2. 捐赠金额
3. campaign_id

我当前的查询不起作用

UPDATE
    tb_campaign AS campaigns
    LEFT JOIN (
        SELECT
            sum(amount_donated) AS amount_donated
        FROM
            tb_donations
        GROUP BY
            campaign_id
    ) AS donations ON
        donations.campaign_id = campaigns.id
SET
    campaigns.total_donations = donations.amount_donated;

我的查询收到错误

Answer 1

您在子查询中错过了campaign_id，因此您的加入无法工作，因为没有donations.campaign_id

UPDATE  tb_campaign AS campaigns
LEFT JOIN (
        SELECT  campaign_id, sum(amount_donated) AS amount_donated
        FROM  tb_donations
        GROUP BY     campaign_id
    ) AS donations ON  donations.campaign_id = campaigns.id
SET    campaigns.total_donations = donations.amount_donated;

但由于您正在寻找数学行，因此您的连接条件应该是内部连接

UPDATE  tb_campaign AS campaigns
INNER  JOIN (
        SELECT  campaign_id, sum(amount_donated) AS amount_donated
        FROM  tb_donations
        GROUP BY     campaign_id
    ) AS donations ON  donations.campaign_id = campaigns.id
SET    campaigns.total_donations = donations.amount_donated;