CREATE FUNCTION getGrade(app_name text, employee_id text, department_id text, category_id integer) RETURNS TEXT
AS $$
BEGIN
  declare grade text = '';

if (employee_id != '')
  select grade = e.grade from public.program_marks_by_employees e
  where e.app_name = app_name and e.employee_id = employee_id
  
  if grade != ''
  	RETURN grade;
	  
  select grade = dep.grade from public.program_marks_by_departments dep
  where dep.app_name = app_name and dep.department_id = department_id

 if grade != ''
  	RETURN grade;

  select grade = c.grade from public.categories c
  where c.id = category_id

  RETURN grade;
END;
$$ LANGUAGE plpgsql;