mysql - php substr function for data varchar -

i have problem, want input data invoice number, when try in phpmyadmin version 5.6.16 in computer working, im upload cpanel phpmyadmin v 5.5 not working.

result in v 5.6.16 :

- inv0001 - inv0002 - inv0003 

result in cpanel/hosting. v 5.5 :

- inv0001 - inv0001 - inv0001 

it's duplicate, how fix it? before.

<?php   $query = "select max(invoice) invoice orders";   $hasil = mysql_query($query);   $data  = @mysql_fetch_array($hasil);   $lastinv = $data['invoice'];   $nextinv= (int) substr($lastinv, 3, 4);   $nextinv++;   $char = "inv";   $newinvoice = $char .  sprintf("%04s", $nextinv); ?> 

you can try below code avoid duplicate records :

$query = "select max(invoice) invoice orders"; $hasil = mysql_query($query); $data  = @mysql_fetch_array($hasil); $lastinv = $data['invoice']; $nextinv= (int) substr($lastinv, 3, 4); $nextinv++; $char = "inv";  $i = 1; while(true) // eliminating duplicacy {     $newinvoice = $char .  sprintf("%04s", $nextinv);      $query = "select * orders invoice = ".$newinvoice;     $hasil = mysql_query($query);     $data  = @mysql_fetch_array($hasil);     if(empty($data))         break;     $i++; }