1054 完全连接中的未知列，但不是其他连接

Question

为什么我会从以下 mysql 语法中收到“1054 未知列错误”：

SELECT attorney_first_name, attorney_last_name, att_school, att_degree_obtained
FROM jos_legalally_attorneys
FULL JOIN jos_legalally_attorney_education
ON jos_legalally_attorneys.user_id=jos_legalally_attorney_education.user_id;

它导致错误：

#1054 - Unknown column 'jos_legalally_attorneys.user_id' in 'on clause' 

我只在尝试FULL JOIN. 使用此确切语法时，所有其他连接（内部、右、左）都将成功。（我已经尝试过这种FULL OUTER JOIN变化）。

Answer 1

这里报告，MySQL不支持FULL JOIN，所以你的查询解释如下：

SELECT attorney_first_name, attorney_last_name, att_school, att_degree_obtained
FROM jos_legalally_attorneys as FULL #FULL is taken as table alias!!
INNER JOIN jos_legalally_attorney_education
ON jos_legalally_attorneys.user_id=jos_legalally_attorney_education.user_id;

现在，由于它具有FULL的表别名jos_legalally_attorneys，因此它无法正常工作。

如果您尝试以下查询，它应该不会给出错误（即使它没有执行您想要的操作）：

SELECT attorney_first_name, attorney_last_name, att_school, att_degree_obtained
FROM jos_legalally_attorneys
FULL JOIN jos_legalally_attorney_education
ON FULL.user_id=jos_legalally_attorney_education.user_id;

现在，为了获得FULL JOINMySQL 下所需的内容，您需要执行以下操作（如下所示）：

SELECT attorney_first_name, attorney_last_name, att_school, att_degree_obtained
FROM jos_legalally_attorneys
LEFT JOIN jos_legalally_attorney_education
ON jos_legalally_attorneys.user_id=jos_legalally_attorney_education.user_id
UNION ALL
SELECT attorney_first_name, attorney_last_name, att_school, att_degree_obtained
FROM jos_legalally_attorneys
RIGHT JOIN jos_legalally_attorney_education
ON jos_legalally_attorneys.user_id=jos_legalally_attorney_education.user_id