What is the employee id of physician John Dorian?
select employeeid from physician where name = "John Dorian"
Find all the prescriptions made by him.
select * from prescribes as t1 join physician as t2 on t1.physician = t2.employeeid where t2.name = "John Dorian"
How many patients' prescriptions are made by him?
select count(t1.ssn) from patient as t1 join prescribes as t2 on t1.ssn = t2.patient join physician as t3 on t2.physician = t3.employeeid where t3.name = "John Dorian"