錯誤代碼：1054未知列

Question

我有以下SQL語句：

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'; 

當我運行它，我得到以下錯誤：

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

爲什麼會出現這個錯誤？

Project_task_id屬於工作表

Image of my efforts table

更新時間：

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

你的語法是錯誤的，它應該是：

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

需要注意的是，據我所知，MySQL是區分大小寫的表名（不在列名上）......這可能會在查詢中造成一些麻煩......？隨着StevieG的校正