>yes i using vfp3.0
>so how to solve the problem?

This case the last SELECT will look differently:

SELECT tmp1.item_name,tmp1.quantity1,tmp2.quantity2 ;
 FROM tmp1,tmp2 ;
 INTO CURSOR tmp3 ;
 WHERE tmp1.item_name=tmp2.item_name ;
 UNION SELECT tmp1.item_name,tmp1.quantity1,0 as quantity2 ;
 FROM tmp1 ;
 WHERE tmp1.item_name NOT IN (SELECT item_name FROM tmp2) ;
 UNION SELECT tmp2.item_name,0 as quantity1,tmp2.quantity2 ;
 FROM tmp2 ;
 WHERE tmp2.item_name NOT IN (SELECT item_name FROM tmp1)