mysql - 带有 "LIMIT 1"的 MySQL SELECT 查询是否可能返回一个集合而不是单个值？

Question

我在使用 CakePHP 的 Containable 行为时遇到了一个奇怪的问题。我有这个:

'contain' => array(
            'ExhibitorTypeRequestType' => array(
                'order' => '(SELECT et.type FROM exhibitor_types AS et WHERE ExhibitorTypeRequestType.exhibitor_type_id = et.id LIMIT 1)',
                'ExhibitorType'
            )
        )

抛出 SQL 错误:

Error: SQLSTATE[42S22]: Column not found: 1054 Unknown column 'SELECT et.type FROM exhibitor_types AS et WHERE ExhibitorTypeRequestType.exhibitor_type_id = et.id LIMIT 1' in 'field list'

有人知道为什么 MySQL 将此查询视为一个列吗？

更新

我在我的项目的其他地方有这个非常相似的查询，也使用 Containable，它工作得很好:

'contain' => array(
            'Field',
            'User' => array(
                'UserField' => array(
                    'order' => '(SELECT f.no_order FROM fields AS f WHERE UserField.field_id = f.id LIMIT 1)'
                )
            )
        )

Answer 1

刚刚发现如果我改变

'contain' => array(
        'ExhibitorTypeRequestType' => array(
            'order' => '(SELECT et.type FROM exhibitor_types AS et WHERE ExhibitorTypeRequestType.exhibitor_type_id = et.id LIMIT 1)',
            'ExhibitorType'
        )
    )

到:

'contain' => array(
            'ExhibitorTypeRequestType' => array(
                'order' => '(SELECT et.type FROM exhibitor_types AS et WHERE ExhibitorTypeRequestType.exhibitor_type_id = et.id LIMIT 1)',
                'ExhibitorType' => array(
                    'order' => 'type'
                )
            )
        )

神奇的效果! 'order' => 'type' 在 ExhibitorType 上下文中是绝对不相关的，它在某种程度上是需要的。否则，Cake 会生成奇怪的 SQL 错误。