kd otomatis

<?php
$pilih = “SELECT kd_roti FROM roti ORDER BY id_roti DESC LIMIT 1″;
/*
//perintah select dikerjakan
$hasil = mysql_query($pilih);
$data = mysql_fetch_array($hasil);
*/
$data=$this->db->query($sql)->row_array();
$potong_kd = substr($data[kd_roti], 2);
$konversi_kd = (int)$potong_kd;
$kd_otomatis = $konversi_kd + 1;
$input=array('kd_roti'=>'R'.$kd_otomatis);