--通过 To_Number 函数异常来判断
CREATE OR REPLACE FUNCTION Is_Number (
   str_    VARCHAR2 ) RETURN VARCHAR2   
IS     
   num_    NUMBER;          
BEGIN     
  num_ := to_number(str_);         
  RETURN 'Y';     
EXCEPTION   
   WHEN OTHERS THEN          
      RETURN 'N';     
END Is_Number;   
/