2. List the primary keys, candidate keys, weak entities (if any), partial keys (if any), total participation and any key constraints
primary keys:
  1. doctor:doctor_id,
  2. Patient:patient_id,
  3. visits:visit_id
  4. Test:test_id
Candidate Keys:
  1. doctor:doctor_id,
  2. Patient:patient_id,
  3. visits:visit_id
  4. Test:test_id
 Weak entities:
There are no weak entities.
Partial Keys : Test_id
Total Participation :
Patient in relationship is primary physician
Test in relationship takes
Constraints:
Cardinatlity constraints:
Doctor to patient in is primary physician: one to one
doctor to visit in attends: one to many
Patient to visit in makes:one to many
Patient to test in takes: one to many