SQL查询从三个不同的表中提取数据

Question

我必须创建一个SQL查询，以按姓，名顺序列出“麻雀”翼中的所有护士。

但是，我需要从Nurse表中拉出Nurse_name和Nurse_surname，该表通过外键Sister_ID链接到另一个名为Sister的表，然后将此表链接到另一个具有外键Sister_ID的表Wing。

护士由姐姐管理，而姐姐则负责管理。

谁能帮助我进行SQL查询吗？ 就这样，我只能从护士和姐妹表中获取数据。

Answer 1

由于您似乎已经意识到应该使用inner join联接来连接表（但显然不需要通过相关列进行连接），因此您应该运用该知识来连接所有需要回答查询的表。

如果您从最终结果开始并往回走，则首先选择所需的列：

select Nurse.Nurse_name, Nurse.Nurse_surname

然后由于它们属于Nurse表，因此在from子句中将其用作源

from Nurse

要获得Wing，您需要连接Sister表，但要连接它和Nurse，首先需要在shared属性上连接SisterNurse表

join SisterNurse on Nurse.Nurse_ID = SisterNurse.Nurse_ID

现在您可以在与SisterNurse共享的属性上加入Sister

join Sister on Sister.Sister_ID = SisterNurse.Sister_Id

最后你可以加入永安

join Wing on Wing.sister_ID = Sister.Sister_ID

将机翼限制为“麻雀”

where Wing.Wing_Name = 'Sparrow'

并排序数据

order by Nurse.Nurse_surname, Nurse.Nurse_name

放在一起，您将获得：

select Nurse.Nurse_name, Nurse.Nurse_surname
from Nurse
join SisterNurse on Nurse.Nurse_ID = SisterNurse.Nurse_ID
join Sister on Sister.Sister_ID = SisterNurse.Sister_Id
join Wing on Wing.sister_ID = Sister.Sister_ID
where Wing.Wing_Name = 'Sparrow'
order by Nurse.Nurse_surname, Nurse.Nurse_name

Answer 2

您不会提供有关所涉及的架构的太多信息，但这可能会有所帮助：

select
  n.Nurse_name
, n.Nurse_surname
, w.Wing_name
, managing_nurse.Nurse_name
, managing_nurse.surname
from
  Nurse n
  join Sister s on n.Sister_ID=n.Sister_ID
  join Wing w on s.Sister_ID=w.Sister_ID
  join Nurse managing_nurse on w.Nurse_Manager_ID=managing_nurse.Sister_ID

Answer 3

一种简单的方法是使用“联合”：

select * from (
select nurse_name, nurse_surname, 'nurse' as nurse_type from nurse_table
   union 
select nurse_name, nurse_surname, 'sister' as nurse_type from syster join nurse_table on nurse_table.syster_id = syster.syster_id
   union 
select nurse_name, nurse_surname, 'wing' as nurse_type from wing join syster on wing.syster_id = syster.syster_id join nurse_table on nurse_table.syster_id =  syster.syster_id )
order by nurse_surname, nurse_name

希望这对您有所帮助！

PS我假设syster表和wing表具有Nurse_name和Nurse_surname字段。 如果不是，则必须为所有选定的列赋予相同的别名