sql我有错误代码：1242子查询返回超过1行

Question

select district,
    city,
    postal_code,
    (
        select sum(amount) as revenue
        from payment,
            address
        group by postal_code
        )
from sakila.address,
    sakila.city,
    sakila.payment
where address.city_id = city.city_id
group by district,
    city,
    postal_code
order by district,
    postal_code;

上面是我的sql语句。我有错误代码1242.我不明白为什么我有错误。我试图通过邮政编码计算总收入，以及填写区，城市，邮政编码。

你能告诉我什么是错的以及如何解决它？

提前谢谢。

Answer 1

尝试以下方法......

SELECT address.district,
       city.city,
       address.postal_code,
       SUM( amount ) AS revenue
FROM address
JOIN city     ON address.city_ID = city.city_ID
JOIN customer ON address.address_ID = customer.address_ID
JOIN payment  ON customer.customer_ID = payment.customer_ID
GROUP BY district, city, postal_code
ORDER BY district, postal_code;

Answer 2

您需要将其设为相关子查询，而不是分组查询。

select district,
    city,
    postal_code,
    (
        select sum(amount) as revenue
        from payment,
            address
        where postal_code = sakila.address.postal_code
        )

您还需要payment和address表之间的连接条件，否则它们将在它们之间创建完整的交叉产品。您还需要主查询中payments表的连接条件。

您应该学习使用ANSI JOIN语法编写查询，然后您不太可能忘记加入条件。而不是使用相关子查询，您只需加入payment。我使用了LEFT JOIN，因此当特定位置没有客户或付款时，您将获得revenu = 0。

完整查询应为：

SELECT district, city, postal_code, IFNULL(SUM(amount), 0) AS revenue
FROM address AS a
JOIN city AS c ON a.city_id = c.city_id
LEFT JOIN customer AS cus ON cus.address_id = a.address_id
LEFT JOIN payment AS p ON p.customer_id = c.customer_id
GROUP BY district, city, postal_code
ORDER BY district, postal_code