how to avoid using temporary?

["I am on the top of the world! Borlange University" <michael3832628@xxxxxxxxx>]

heres my sql query:
EXPLAIN SELECT t1.szs_guige,SUM(t1.szs_shuliang) FROM szs_ck_ruku_items
t1,szs_ck_ruku t2 WHERE t1.szs_rukubianhao = t2.szs_rukubianhao AND
t2.szs_date>'2010-10-23' GROUP BY t1.szs_guige ORDER BY null

result:

id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t2 range PRIMARY,date date 3 \N 177 Using where; Using index; Using
temporary
1 SIMPLE t1 ref PRIMARY PRIMARY 32 szs_jihuadan.t2.szs_rukubianhao 4

table structure below:
CREATE TABLE `szs_ck_ruku` (
  `szs_rukubianhao` varchar(10) NOT NULL,
  `szs_kuhao` varchar(10) NOT NULL,
  `szs_kuwei` varchar(10) NOT NULL,
  `szs_xianghao` varchar(4) NOT NULL,
  `szs_caozuoyuan` varchar(10) NOT NULL,
  `szs_date` date NOT NULL,
  PRIMARY KEY  (`szs_rukubianhao`,`szs_kuhao`,`szs_kuwei`),
  KEY `date` (`szs_date`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8
CREATE TABLE `szs_ck_ruku_items` (
  `szs_rukubianhao` varchar(10) NOT NULL,
  `szs_kuhao` varchar(10) NOT NULL,
  `szs_kuwei` varchar(10) NOT NULL,
  `szs_shengchanhao` varchar(50) NOT NULL,
  `szs_guige` varchar(100) NOT NULL,
  `szs_tuhao` varchar(100) NOT NULL,
  `szs_shuliang` int(8) NOT NULL,
  `szs_beizhu` text NOT NULL,
  PRIMARY KEY  (`szs_rukubianhao`,`szs_kuhao`,`szs_kuwei`,`szs_shengchanhao`,`szs_guige`,`szs_tuhao`),
  KEY `GG` (`szs_guige`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8


how to avoid using temporary? i am confuzed......

thanks