title: How to create a zero or one to many relationship in Mysql workbench
body: <p>In a database that have Orders, Customers tables, i need the relation between these two tables to be zero or one to many relationship, simply because in my application, an order can exist without being assigned to a customer.</p>
  
  <p>One first idea that comes to my mind is to make the foreign key nullable, this way when creating an order the foreign key can be null, but i don't know how to do so.
  I'm working on a model so i can render it to my 'teacher', so i need to know how to do it using the EER diagram.</p>
  
  <p>thanks in advance.</p>