код в студию)

первый запрос
SELECT SUM(kolich) FROM rashodni
WHERE nomenkl_name='$nomenkl_name' AND ( vid_doc='наряд' OR vid_doc='разнорядка')
AND poluch_podr='$id_podr' AND status_doc='исполнен' AND info_doc='1'
второй запрос
SELECT SUM(kolich) FROM rashodni WHERE nomenkl_name='$nomenkl_name' AND otprav_podr='$id_podr'
AND status_doc='исполнен' AND info_doc='1'

два в одном)

$sql = mysql_query("SELECT SUM(`a`.`kolich`) AS `one`, SUM(`b`.`kolich`) AS `two`, (SUM(`a`.`kolich`) - SUM(`b`.`kolich`)) AS `result` 
                    FROM `rashodni` AS `a`
                    LEFT JOIN `rashodni` AS `b` ON `b`.`otprav_podr` = `a`.`poluch_podr`
                       WHERE `a`.`nomenkl_name` = '".$nomenkl_name."' 
                           AND (`a`.`vid_doc` = 'наряд' OR `a`.`vid_doc` = 'разнорядка') 
                           AND `a`.`poluch_podr` ='".$id_podr."' 
                           AND `a`.`status_doc` = 'исполнен' 
                           AND `info_doc` = 1");
$res = mysql_fetch_assoc($sql);
echo "<pre>";
print_r($res);
echo "</pre>";