Question

Consider the following relational database schema-

Doctor(SSN,FirstName,LastName,Speciality,YearsOfExperience,PhoneNum)

Patient(SSN,FirstName,LastName,Address,DOB,PrimaryDoctor_SSN)

Medicine(TradeName,UnitPrice,GenericFlag)

Prescription(Id,Date,Doctor_SSN,Patient_SSN)

Prescription_Medicine(Prescription_Id,Trade_Name,NumOfUnits)

Write Relational Algebra expression for the following:

List the first and last name of patients whose primary doctor named “Rahul kumar”

List the first and last name of doctors who are not primary doctors of any patient

List the first and last name of patients who have no prescription written by doctors other than the primary doctors

List the trade name of generic medicine with unit price greater than Rs. 50

List the SSN of Patients who have “Disprin” prescriped to them by doctor name “Suresh Verma”

find average YearsofExperience based on Speciality of doctors

Answer 1

1.

$\pi$ _{Patient.FirstName,Patient.LastName}( _{PrimaryDoctor_SSN = 'Rahul Kumar'} Patient $\Join$ _{PrimaryDoctor_SSN = SSN} Doctor)

2.

$\pi$ _{Doctor.FirstName,Doctor.LastName}( _{PrimaryDoctor_SSN != SSN​} Patient $\Join$ Doctor)

here $\Join$ is theta join not equi join

3.

$\pi$ _{Patient.FirstName,Patient.LastName}( Patient $\Join$ _{PrimaryDoctor_SSN = SSN} Doctor $\Join$ _{SSN = Doctor_SSN} Prescription)

4.

$\pi$ _{Medicine.TradeName}( _{UnitPrice > 50}    Prescription_Medicine $\Join$ _{Trade_Name = TradeName} Medicine )

5.

$\pi$ _Patient.SSN( _{Trade_Name = 'Disprin' and Doctor.FirstName = 'Suresh' and Doctor.LastName = 'Verma'} Patient $\Join$ _{PrimaryDoctor_SSN = SSN} Doctor $\Join$ _{SSN = Doctor_SSN} Prescription)

6.

$\pi$ _{avg(YearsOfExperience) group by Specilality}(Doctor )

Do ask if any doubt. Please upvote.