mysql - 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，我几乎完成了，但我不太明白为什么每当我尝试包含 employee 时结果会变成空。表。

这是我的原话:

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 时语句，结果返回空，
以下是更新后的声明:

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;

我想也许我弄乱了最后一个 JOIN 语句，但 JOIN 不应该像 JOIN table2 ON table1.Primarykey=table2.foreignkey 一样吗？ 。但也许我错了，有人可以指出我的错误吗？我真的很困惑

Answer 1

像这样尝试一次

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;