SQL查询从三个不同的表中提取数据

Question

I have to create a SQL query to list all the Nurses in the 'Sparrow' Wing ordered by last name, first name.

However, I need to pull Nurse_name and Nurse_surname from the Nurse table, which is linked to another table called Sister by the foreign key Sister_ID, this table is then linked to another table called Wing which has the foreign key Sister_ID.

The nurse is managed by the sister and the sister manages the wing.

Can anyone help me with an SQL query for this? As it is, I am only able to get the data from nurse and sister tables.

Answer 1

Since you seem to be aware that you should use the inner join to connect tables (but apparently not that the connection needs to be via the related columns) you should apply that knowledge to connect all the tables you need to answer the query.

If you start at the end result and work your way backwards you first chose the columns you need:

select Nurse.Nurse_name, Nurse.Nurse_surname

and then as they belong to the Nurse table you use that as source in the from clause

from Nurse

to get the Wing you need to connect the Sister table, but to connect that and Nurse you first need the SisterNurse table joined on the shared attribute

join SisterNurse on Nurse.Nurse_ID = SisterNurse.Nurse_ID

now you can join Sister on the attribute shared with SisterNurse

join Sister on Sister.Sister_ID = SisterNurse.Sister_Id

and finally you can join Wing

join Wing on Wing.sister_ID = Sister.Sister_ID

limit the Wings to the one names 'Sparrow'

where Wing.Wing_Name = 'Sparrow'

and order the data

order by Nurse.Nurse_surname, Nurse.Nurse_name

Put it all together and you get:

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

You don't give much information about the schema involved but maybe this will help:

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

A simple way is to use 'union':

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

Hope this help you!

PS I assume that syster and wing tables have nurse_name and nurse_surname fields. If not you have to give the same alias to all the selected columns