how to avoid using temporary?

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