Schema Diagrams 

Multiple columns in a table can contribute to the overall Primary Key. For example, in the Classroom table he has 'building' and 'room_no' working together to form the primary key. So you can have the same building # listed, as long as each of the room #'s are unique within that building. Similarly, the same room # can be used, but only if that room # appears in unique building #'s. So, when the two columns are combined, the following entries are each unique within the table: Building 1, Room 1 Building 1, Room 2 Building 2, Room 1 Building 2, Room 2 Since the 2 columns work together as the Primary Key, you could NOT have: Building 1, Room 1 Building 1, Room 1 (

Study from books

Follow neso academy