Mysql更新和连接查询

Question

我在使用 Sum 更新查询时遇到问题。我有两张桌子活动和捐款。我想更新特定活动的每笔捐款总额

tb_campaign

1. 身份证
2. 姓名
3. total_donations

tb_donations

1. 身份证
2. amount_donated
3. campaign_id

我当前的查询不工作

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;

我的查询出现错误

Answer 1

如果要根据匹配记录更新tb_campaign.total_donations 中的列，请尝试以下更新查询。

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;

如果您需要更新 tb_campaign 表中与 total_donations 不匹配的所有列，试试这个， 注意： “column total_donations cannot be null”添加了coalesce以避免null

UPDATE tb_campaign AS campaigns
        LEFT JOIN
    (SELECT 
        campaign_id,
            COALESCE(SUM(amount_donated), 0) 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;

Answer 2

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;