Question

我有一个查询，当只有一种类型的“按组”响应时，它会精确返回我想要的内容。如果存在多个错误，则会出现“子查询返回多于1行”错误。

我尝试了多种结构化查询的方法，包括使用“ in”，但无济于事。

SELECT 
    (
    SELECT substring(postcode, 1, locate (' ', postcode) - 1)
    FROM user_locations AS ul
    JOIN users AS u ON u.id = ul.user_id
    WHERE u.membertype = "customer"
    ) AS postcode,
    (
    SELECT count(u.membertype)
    FROM users AS u
    JOIN user_locations AS ul ON u.id = ul.user_id
    WHERE u.membertype = "cook"
    GROUP BY ul.postcode

    ) AS cook,
    (
    SELECT count(u.membertype)
    FROM users AS u
    JOIN user_locations AS ul ON u.id = ul.user_id
    WHERE u.membertype = "customer"
    GROUP BY ul.postcode
    ) AS customer

我希望看到的多个邮政编码

Postcode | Cooks | Customers
G83      | 12    | 34 
G84      | 19    | 76
G85      | 10    | 50

Answer 1

您可以使用表达式u.membertype=xxx在单个查询中执行此操作，如果为true，则为1，否则为0。

SELECT ul.postcode AS "Postcode",
       SUM(u.membertype="cook") as "Cooks"
       SUM(u.membertype="customer") as "Customers"
FROM users AS u
JOIN user_locations AS ul ON u.id = ul.user_id
GROUP BY ul.postcode

如果存在两种以上成员类型，则可以添加WHERE u.membertype IN ("cook","customer")。

修复“子查询返回多于1行”的错误

1 个答案: