rpad(str, len, pad) - Returns str, right-padded with pad to a length of len
If str is longer than len, the return value is shortened to len characters.
Example:
  > SELECT rpad('hi', 5, '??') FROM src LIMIT 1;
  'hi???'  > SELECT rpad('hi', 1, '??') FROM src LIMIT 1;
  'h'
