Table company {
  id int PK
  address_id int
  name varchar
}

Table department {
  id int PK
  name varchar
  parent_department_id int
  company_id int
}

Table address {
  id int PK
  street varchar
  house_number varchar
  apartment_number int
  zip_code varchar
  country varchar
}

Table email {
  id int PK
  value varchar
}

Table telephone {
  id int PK
  value varchar
  type varchar
}

Table employee {
  id int PK
  first_name varchar
  last_name varchar
}

// tabele n:m

Table employee_emial_link {
  id int PK
  employee_id int
  email_id int
}

Table employee_telephone_link {
  id int PK
  employee_id int
  telephone_id int
}

Ref: company.address_id > address.id

Ref: department.parent_department_id > department.id
Ref: department.company_id > company.id

Ref: employee_emial_link.employee_id > employee.id
Ref: employee_emial_link.email_id > email.id

Ref: employee_telephone_link.employee_id > employee.id
Ref: employee_telephone_link.telephone_id > telephone.id

// Ref: orders.user_id > users.id

// Ref: order_items.order_id > orders.id

// Ref: order_items.product_id > products.id

// Ref: products.merchant_id > merchants.id

// Ref: users.country_code > countries.code

// Ref: merchants.admin_id > users.id

// Ref: merchants.country_code > countries.code