Design an E/R diagram for the following situation: Doctors prescribe drugs for patients. A given doctor can prescribe many drugs for a certain patient. Sometimes a doctor may not prescribe any drug to a patient. Many doctors can treat a patient. Many doctors can prescribe the same drug to the same patient. A prescription can involve more than one patient (e.g., a mother and her baby) and more than one drug, but is associated with a unique doctor.
This problem may be trickier than it appears. Carefully consider what the instances of each entity set and relationship in your E/R diagram will look like.