I want to sort an alphanumeric values for the employee ids. For this I have writen the query in the code as :

def _generate_order_by(self,employee_id,query):        
          my_order = "SELECT employee_id FROM hr_employee order by CAST(SPLIT_PART(employee_id, '-', 2) AS INTEGER)"       
          if employee_id:             
             return super(hr_employee, self)._generate_order_by(x_payroll, query) + ", " + my_order            
          return " order by " + my_order

Here I call the function as default,

_defaults = {

                   'employee_id': _generate_order_by, 

                   }  

But while running this code,the folllowing error occured :

ProgrammingError: syntax error at or near "SELECT"

If there is any error in this code please help me to correct.