多JOIN語句

Question

我試圖檢索階段，批處理，任務和員工分配到一個項目的任務，我差不多完成，但我不明白爲什麼結果變爲空時，只要我試圖包括employee表。

這是我原來的語句：

SELECT project.JONumber, stage.StageName, batch.BatchName, tasks.task_name, tasks_assignment.employee_number 
    FROM project 
    JOIN stage ON project.id = stage.project_id 
    JOIN batch ON stage.ID = batch.stage_id 
    JOIN tasks ON batch.id = tasks.batch_id 
    JOIN tasks_assignment ON tasks.id = tasks_assignment.task_id 
    WHERE project.id = 23441; 

但是當我嘗試添加其他JOIN聲明，結果返回空，
這裏是更新語句：

SELECT project.JONumber, stage.StageName, batch.BatchName, tasks.task_name, tasks_assignment.employee_number, employee.FirstName 
FROM project 
JOIN stage ON project.id = stage.project_id 
JOIN batch ON stage.ID = batch.stage_id 
JOIN tasks ON batch.id = tasks.batch_id 
JOIN tasks_assignment ON tasks.id = tasks_assignment.task_id 
JOIN employee ON employee.ID=tasks_assignment.employee_number 
WHERE project.id = 23441; 

我我認爲我可能搞砸了最後一個JOIN語句，但不是JOIN應該像JOIN table2 ON table1.Primarykey=table2.foreignkey。但也許我錯了，有誰能指出我的錯誤嗎？我只是真的很困惑

Answer 1

嘗試這樣一次

SELECT project.JONumber, stage.StageName, batch.BatchName, tasks.task_name, tasks_assignment.employee_number, employee.FirstName 
FROM project 
JOIN stage ON project.id = stage.project_id 
JOIN batch ON stage.ID = batch.stage_id 
JOIN tasks ON batch.id = tasks.batch_id 
JOIN tasks_assignment ON tasks.id = tasks_assignment.task_id 
RIGHT OUTER JOIN employee ON employee.ID=tasks_assignment.employee_number 
WHERE project.id = 23441;