CREATE OR REPLACE FUNCTION checkBankCard(p_bankcard IN varchar2)
  RETURN     varchar2   --正确时返回ok，否则返回正确的校验码
 IS
  curval NUMBER := 0;
  total      NUMBER := 0;
  everyother NUMBER := 1;
  v_end number;
BEGIN
  IF (p_bankcard IS NULL) then
    RETURN ‘null‘;
  end IF;
  FOR i IN reverse 1 .. (LENGTH(p_bankcard) - 1) loop
    curval := SUBSTR(p_bankcard, i, 1);
    IF everyother = 1 then
      everyother := 0;
      curval     := curval * 2;
      IF (curval > 9) then
        curval := curval - 9;
      end IF;
    else
      everyother := 1;
    end IF;
    total := total + curval;
  end loop;
  IF MOD(total, 10) = 0 THEN
    v_end := 0;
  ELSE
    v_end:= 10 - MOD(total, 10);
  END IF;
  if to_char(v_end) = substr(p_bankcard,lengthb(p_bankcard),1) then
     return ‘ok‘;
  else
     return to_char(v_end);
  end if;
end;

校验银行卡号正确性的oracle源代码