select b.sname,c.sname as csname,a.qty,a.label
from tb2 a join tb1 b on a.scode = b.scode
           join tb1 c on a.scode_dist = c.scode

------解决方案--------------------
SQL code
select b.sname,c.sname,a.qty, a.label from tb2 a  left join tb1 b on a.scode =b.scode
                                          left join tb1 c on a.scode_dist =c.scode

------解决方案--------------------
SQL code

select 
    b.sname,c.sname as csname,a.qty,a.label
from 
    tb2 a 
full join 
    tb1 b 
on 
    a.scode = b.scode
full join 
    tb1 c 
on 
    a.scode_dist = c.scode