what will be the sql query code of this "Healthcare" database? - mysql

Question

SQL Query:
Write a SQL statement to display the SSN & name of patients who are younger than the average of all patients.
Write a SQL statement to display the name and age of the oldest patients along with his or her doctor's name.
write a SQL statement to display all of the patients who are prescribed with vitamins and below 50 years old.
display the name of most experienced heart specialist.
Solution: I have completed these answers of those questions but not sure it's okay or not. Please help me if there is any wrong or need any correction.
1.)
select SSN, Name
from patient
where age < (
select avg(age)
from Patient
);
2.)
select patient.name, max(patient.age), patient.DName
from Patient
join Doctor
where patient.primary_DoctorID = Doctor.DoctorID;
3.)
SELECT Patient.Name, Patient.age
from Patient
where patient.age < '50' and Patient.Primary_DoctorID = (
SELECT Prescription.DoctorID
from Prescription
where Prescription.P_ID = (
select Prescription_Medicine.P_ID
FROM Prescription_Medicine
where Prescription_Medicine.Tradename = 'Vitamin' )
);
Q3 returns
subquery returns more than one row
SELECT dname
FROM doctor
IN speciality = 'Heart' AND experience = (
SELECT MAX(doctor.experience)
FROM doctor
GROUP BY speciality;
);

Answer 1

Update your 3rd query to -
SELECT Patient.Name, Patient.age
from Patient
where patient.age < '50'
and EXISTS (
SELECT Prescription.DoctorID
from Prescription
where Patient.Primary_DoctorID = Prescription.DoctorID
and Prescription.P_ID = (
select Prescription_Medicine.P_ID
FROM Prescription_Medicine
where Prescription_Medicine.Tradename = 'Vitamin' )
);
And update your 4th query to -
SELECT dname
FROM doctor d
JOIN (SELECT speciality, MAX(doctor.experience)
FROM doctor
GROUP BY speciality) d1 on d.speciality = d1.speciality
WHERE speciality = 'Heart'

Answer 2

--USING MS-SQL SERVER FOR THE 4TH QUERY
--YOU CAN ALSO USE WINDOW FUNCTION TO SOLVE THE FOURTH
--QUERY.
--USING CTE (COMMON TABLE EXPRESSION)
WITH CTE
AS
(
SELECT
D.DNAME,
DENSE_RANK() OVER (PARTITION BY D.DNAME ORDER BY
D.EXPERIENCE DESC) AS RNK
FROM DOCTOR
WHERE SPECIALITY = 'HEART'
)
SELECT DNAME FROM CTE
WHERE RNK = 1