Relationship design for areas, managers and general manager
It's ok to have an &quot;ALL&quot; value as an Area but it might be preferable and more flexible to add a third table, as a linking table, called EmployeeArea instead.
The EmployeeArea table is where you can store the area_id and employee_id (as manager_id), to represent the technically many-to-many relationship between the tables. Then the boss of all areas would have a record in there for each Area.
This is more normalized of a design, and is more flexible if for some reason there needs to be multiple bosses of all areas, or special cases where multiple employees are responsible for the same area.