employee id already exits

DECLARE
    v varchar2(6);
BEGIN
    SELECT EMP_ID INTO V FROM EMP_MAST WHERE EMP_ID=:emp_mast.EMP_ID;
    IF V >0 THEN
        MESSAGE('Employee ID Already Exist !!');
        MESSAGE('Employee ID Already Exist !!');   
    else
        next_field;
    end if;
    exception when others then raise form_trigger_failure;
       
end;