MySQL说该列不明确

Question

我需要在MySQL表上的相同字段上进行查询，但使用不同的参数。这是我的查询。出现的问题是MySQL说用户名是不明确的。

SELECT projects_id, 
projects_users_id,projects_companies_id,projects_name,
projects_description,project_registered_date,
projects_users_id_register,
users.users_name as userInCharge,companies.companies_name as company,
users.users_name as user_register FROM projects 
LEFT JOIN users as userInCharge ON (users_id = projects_users_id) 
LEFT JOIN users as register ON (users_id=projects_users_id_register)
LEFT JOIN companies ON (companies_id = projects_companies_id) ORDER BY projects_id DESC 

我的目标是获取项目负责人和注册项目人员的ID。我该怎么做？

Answer 1

由于这些LEFT JOIN条款，您的含糊不清：

LEFT JOIN users as userInCharge ON (users_id = projects_users_id) 
LEFT JOIN users as register ON (users_id=projects_users_id_register)

您需要指定users_id的来源（是的 - 我知道它们来自同一个表，但有时SQL有点慢）尝试：

LEFT JOIN users as userInCharge ON (userInCharge.users_id = projects_users_id) 
LEFT JOIN users as register ON (register.users_id=projects_users_id_register)

Answer 2

使用表别名而不是users.users_name。

还有加入。

Answer 3

您与users表格userInCharge和register一起加入，因此在指定列时使用这些名称

userInCharge.users_name as userInCharge
register.users_name as user_register

而不是

users.users_name as userInCharge
users.users_name as user_register