Question

您好我有以下实体：

表格USER ：

id_user Name Username role

表格TASK ：

id_task task_Name tipe

TABLE COMPLETED_TASK ：

id_task id_user

表格ASSIGNED_TASK ：

id_task id_user

有没有办法获得完整的任务列表“已完成并已分配”以及相应的用户？

我尝试了以下查询，但这并不完全正常，因为它无法返回所有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

sql join 4表并返回所有字段

1 个答案: