create or replace function left_pad
(base_string in varchar2,
new_length in integer,
pad_string in varchar2) return varchar2
is
begin
return lpad
(base_string,greatest(length(base_string),new_length),pad_string);
end left_pad;
greatest(length(base_string),new_length)
length(base_string)和new_length比較，值就是那個最大的值