多个JOIN语句

Question

我正在尝试检索分配给项目任务的阶段，批处理，任务和员工，我几乎已经完成了但是我无法理解为什么每当我尝试包含employee表。

这是我原来的陈述：

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;

但是当我尝试添加另一个JOIN语句时，结果返回空，
这是更新后的声明：

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;

我想，也许我搞砸了最后的JOIN声明，但并不是说JOIN应该像JOIN table2 ON table1.Primarykey=table2.foreignkey一样。但也许我错了，有人能指出我的错误吗？我真的很困惑

Answer 1

尝试这样一次

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;