title: Can an entity have multiple primary keys? ER Model
body: <p>I understand that a primary key is a column that uniquely identifies every row in a database table. Therefore you can have only one primary key in your entity. However, in my textbook it an entity contains its own PK and another PK that is also a foreign key from the related entity. My question is if you are sharing a primary key then can you have more than one? If so, do the 2 primary keys form a one primary key? Or are they on their own individual identifiers for that entity.</p>
  
  <p><a href="https://i.stack.imgur.com/vHSLZ.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/vHSLZ.png" alt="enter image description here"></a></p>
  
  <p>For example, the PK of COURSE entity is also a foreign key and a PK of the CLASS entity. Also, CLASS entity now has 2 PKs.</p>