How to retrieve data solely by foreign key in MySQL? - mysql

Question

The mission: Visualize the patients that were treated by surgeons.
Table: patients
id_patient
name
last_name
Table: doctors
id_doctor
name
last_name
speciality ("surgeon" is one of the possibilities)
Table: visits
id_visit
id_patient_fk (foreign key)
id_doctor_fk (foreign key)
With the id_doctor_fk pointing to id_doctor, I have to see if that doctor is a surgeon, right? Is this possible? I gave up, so I ask.

Answer 1

If you want patients who have seen a surgeon, you can use exists:
select p.*
from patients p
where exists (select 1
from visits v join
doctors d
on d.id_doctor = v.id_doctor_pk
where v.id_patient_fk = p.id_patient and
d.specialty = 'surgeon'
);

Answer 2

i created an example for your question . i hope this is help you:
CREATE TABLE #patients2 (
id_patient int,
[name] VARCHAR(100),
last_name VARCHAR(100)
);
CREATE TABLE #doctors2 (
id_doctor int,
[name] VARCHAR(100),
last_name VARCHAR(100),
speciality VARCHAR(100),
);
CREATE TABLE #dvisits2 (
id_visit int,
id_patient_fk int,
id_doctor_fk int
);
--drop table #table1
INSERT INTO #patients2
(id_patient, [name], last_name)
VALUES
(1,'patient1','last_name1'),
(2,'patient2','last_name2'),
(3,'patient3','last_name3'),
(4,'patient4','last_name4'),
(5,'patient5','last_name5'),
(6,'patient6','last_name6'),
(7,'patient7','last_name7'),
(8,'patient8','last_name8');
INSERT INTO #doctors2
(id_doctor, [name], last_name, speciality )
VALUES
(1,'doctor1','last_name1','surgeon'),
(2,'doctor2','last_name2','not surgeon'),
(3,'doctor3','last_name3','surgeon'),
(4,'doctor4','last_name4','not surgeon'),
(5,'doctor5','last_name5','surgeon'),
(6,'doctor6','last_name6','surgeon'),
(7,'doctor7','last_name7','not surgeon'),
(8,'doctor8','last_name8','surgeon');
INSERT INTO #dvisits2
(id_visit, id_doctor_fk,id_patient_fk)
VALUES
(1,1,1),
(2,2,2),
(3,3,3),
(4,4,4),
(5,5,5),
(6,6,6),
(7,7,7),
(8,8,8);
select * from #patients2 p
join #dvisits2 dv on p.id_patient = dv.id_patient_fk
join #doctors2 doc on dv.id_doctor_fk = doc.id_doctor
where doc.speciality = 'surgeon'
result =
id_patient [name] last_name id_visit id_patient_fk id_doctor_fk speciality id_doctor [name] last_name
1 patient1 last_name1 1 1 1 surgeon 1 doctor1 last_name1
1 patient1 last_name1 1 1 1 surgeon 1 doctor1 last_name1
3 patient3 last_name3 3 3 3 surgeon 3 doctor3 last_name3
3 patient3 last_name3 3 3 3 surgeon 3 doctor3 last_name3
5 patient5 last_name5 5 5 5 surgeon 5 doctor5 last_name5
6 patient6 last_name6 6 6 6 surgeon 6 doctor6 last_name6
8 patient8 last_name8 8 8 8 surgeon 8 doctor8 last_name8