Oxid simple sql memory exhausted?

Hey people… I have a question…

I have a very VERY simple sql-query, which somehow causes to exhaust the memory limit. Like… how to F does this even work?

Here is my code:
$sSql = "SELECT bonusCode, timestamp FROM bonusCodes WHERE ordernum ='" . $ordernum . "'";
        $rs = $oDb->Execute($sSql);
        while(!$rs->EOF) {
            $aPaycodes[] = $rs->fields[0];
            // $rs->moveNext();

Please help. Am I missing something really important for such a simple query? I have 128MB memory_limit.
There is no other query running.

First of all I would miss:

 $rs = [B]oxDb::getDb()->[/B]execute($sSql);