mysql - sql连接4个表并返回所有字段

Question

您好，我有以下实体:

表用户:

id_user
姓名
用户名
作用

表任务:

id_task
任务名称
提示

表 COMPLETED_TASK:

id_task
id_user

表ASSIGNED_TASK:

id_task
id_user

有什么方法可以获取任务的完整列表“已完成并分配”以及相应的用户？

我尝试了以下查询，但这并不完全有效，因为它未能返回所有 TASK.id_task

SELECT * FROM TASK 
LEFT  OUTER  JOIN COMPLETED_TASK ON TASK.id_task=COMPLETED_TASK.id_task 
LEFT  OUTER    JOIN ASSIGNED_TASK  ON TASK.id_task=ASSIGNED_TASK.id_task 
INNER    JOIN USER ON USER.id_user=ASSIGNED_TASK.id_user 
OR USER.id_user=COMPLETED_TASK.id_user 

Answer 1

the real problem, is that sql join or more exactly left join,
return all the left table rows,
but return null value for the fieldset, that   not have match in ON clause.

so i must fill a table whit all task,whit this  head
<thead><th>id_task</th><th>Nametask</th><th>Assigned to</th>th>Tipology</th>

and i need for all task the fiedset id_task for edit and delete task.
so seems evry type of join dont give this result whats that the impossiblequery