The below SQL to Sort character field as int,

select *  from table_name order by cast(employees_id as int) asc

But in python the same code _order = "cast(employees_id as int) asc"  is not support.

Solution to override _generate_order_by method in python,

def _generate_order_by(self, order_spec, query):
        my_order = "cast(employees_id as int) asc"            
        if order_spec:
            return super(class_name, self)._generate_order_by(order_spec, query) + ", " + my_order
        return " order by " + my_order

Refer the link for more details.