>Give to me the Visits,Doctors PK fields
>( This is an information to put always in the UT's threads)

Visits doesn't have a PK. I don't know, why it's designed this way. I'll speak with my colleague about it.

The table Patients has Patient_Name as PK

The table Doctors has Doctor_Name as PK and Doctor_Name + Doctor_Specialty is a candidate key, in other words you can not have a doctor with multiple specialties.

Visits have Visit_Date field, Patient_Name, Doctor_Name fields and some other fields such as amount_charged, etc.