错误代码：1054。未知列

Question

我有以下SQL语句：

SELECT efforts.user_id, project_tasks.task_name, sum(hours) 
FROM efforts, users, project_tasks
INNER JOIN PROJECT_TASKS pu ON efforts.project_task_id = pu.id  
INNER JOIN USERS u ON efforts.users_id = u.id
WHERE project_tasks.project_id = '2'; 

当我运行它时，我收到以下错误：

Error Code: 1054. Unknown column 'efforts.project_task_id' in 'on clause'

为什么我收到此错误？

Project_task_id属于努力表

Image of my efforts table

更新：

SELECT u.full_name, pu.task_name, hours 
FROM efforts
INNER JOIN project_tasks pu ON efforts.project_task_id = pu.id   
INNER JOIN users u ON efforts.user_id = u.id 
GROUP BY user_id, task_name

Answer 1

你的语法错了，它应该是：

SELECT efforts.user_id, pu.task_name, sum(hours)  
FROM efforts
INNER JOIN PROJECT_TASKS pu ON efforts.project_task_id = pu.id   
INNER JOIN USERS u ON efforts.user_id = u.id 
WHERE pu.project_id = '2';  

Answer 2

请注意，据我所知，MySQL对表名称（而不是列名称）区分大小写......这可能会导致查询出现问题......？随着StevieG的纠正