Question

此问题是Is there a standard way to swap a query from an ID to a different column like 'name'?

的后续问题

此查询正常工作：

    SELECT manufacturers.id, manufacturers.name, models.model_manufacturer, models.model_part
    FROM models 
    INNER JOIN manufacturers 
    ON manufacturers.id = models.model_manufacturer
    WHERE model_part = (
        SELECT parts.id 
        FROM parts 
        WHERE parts.name = '{$part_name}')
    GROUP BY manufacturers.id
    ORDER BY name ASC

但是当遇到具有多个模型的制造商时，这个失败并且“子查询返回超过1行”：

SELECT parts.id, models.id, models.model_part, models.model_manufacturer, models.name, models.year, models.weight
    FROM parts
    INNER JOIN models
    ON parts.id = models.model_part
    WHERE model_manufacturer = (
        SELECT manufacturers.id 
        FROM manufacturers 
        WHERE manufacturers.name = '{$manufacturer_name}') 
    && model_part = (
        SELECT parts.id 
        FROM parts 
        WHERE parts.name = '{$part_name}')

我真正理解的是，如果我只运行工作示例中的子查询，或者在第二个示例中单独运行子查询，它们都会返回单个值。如果我运行整个查询，它们都返回多个值。那么为什么一个错误而另一个错误呢？它可以在myPHPAdmin中正常运行查询，但在我尝试在PHP文件中执行时失败。

Answer 1

但是这个，当它遇到一个拥有超过一个的制造商单个模型，失败，“子查询返回超过1行”

MySQL =运算符可以将1个值与另一个值进行比较。当子查询返回更多，然后是1值时，它会混淆，因为它不知道，可以与之进行比较。

使用IN运算符代替=：

SELECT parts.id, models.id, 
    models.model_part, models.model_manufacturer, 
    models.name, models.year, models.weight
FROM parts
INNER JOIN models
ON parts.id = models.model_part
WHERE model_manufacturer = (
        SELECT manufacturers.id 
        FROM manufacturers 
        WHERE manufacturers.name = '{$manufacturer_name}') 
    && model_part IN (
        SELECT parts.id 
        FROM parts 
        WHERE parts.name = '{$part_name}')

对不起，如果我把IN操作员放到错误的位置。但我认为，model_part的第二个子查询是正确的位置。

Answer 2

IN的上述建议可能是最简单的想法。

我很想将它重新编码为JOIN，但使用DISTINCT删除重复项： -

SELECT DISTINCT parts.id, models.id, models.model_part, models.model_manufacturer, models.name, models.year, models.weight
    FROM parts
    INNER JOIN models
    ON parts.id = models.model_part
    INNER JOIN manufacturers
    ON models.model_manufacturer = manufacturers.id AND manufacturers.name = '{$manufacturer_name}'
    INNER JOIN parts parts2 ON models.model_part = parts2.id AND parts.name = '{$part_name}'

试图更好地理解MYSQL子查询并返回超过1行

2 个答案: