DB_common::rollback()

<?php
// Once you have a valid DB object named $db...

$db->autoCommit(false);

$db->query('INSERT INTO blah (a) VALUES (11)');

$res =& $db->query('SELECT b FROM blue');
if (DB::isError($res)) {
    echo $res->getMessage() . "\n";
}
while ($res->fetchInto($row, DB_FETCHMODE_ORDERED)) {
    if ($row[0] == 'problem') {
        $db->rollback();
    }
}
$res->free();

$db->query('DROP TABLE blah');
$db->commit();
?>