title: Users, Customers, Tenants, Employees - All in the same table?
body: <p>In this case let me be more specific about the problem</p>
  
  <p>I've got a peoples table(with customer &amp; supplier) and I've got a users table(for users who can login). </p>
  
  <p>Currently I have this DB structure</p>
  
  <p>Customers -> Organisations -> linked through rel_customer_addresses to address table.
  (as 1 customer could have delivery_address, invoice address etc.)</p>
  
  <p>Users -> Tenants -> linked through rel_users_addresses to the address table 
  (as 1 user could have delivery_address, invoice address etc.)</p>
  
  <p>Now I've got in the invoice table customer_key. The problem is when the user himself is the customer and the invoice is from one of his customers. How do I indicate my web app to look up user and not the customer?</p>