select t1.id_good,t1.product_name,t2.p_cnt,t2.p_sum,t3.s_cnt,t3.s_sum
from
(
  select id_good,product_name from buying
  union
  select id_good,product_name from selling
) t1
left join
(
  select id_good,product_name,sum('quantity_buying') p_cnt,sum('summ_good_buying') p_sum
  from buying
  group by id_good,product_name
) t2
left join
(
  select id_good,product_name,sum('quantity_order') s_cnt,sum('summ_good_order') s_sum
  from selling
  group by id_good,product_name
) t3
on t1.id_good=t2.id_good and t1.product_name=t2.product_name
on t1.id_good=t3.id_good and t1.product_name=t3.product_name

SELECT t1.id_good,t1.product_name
    ,t2.sum_quantity_buying,t2.s_summ_good_buying 
    ,t3.sum_quantity_order,t3.s_summ_good_order
FROM
(
  select id_good id_good,product_name product_name from buying
  union
  select id_good id_good,product_name product_name from selling
) t1
LEFT JOIN
(
  SELECT id_good,product_name,SUM(`quantity_buying`) sum_quantity_buying,SUM(`summ_good_buying`) s_summ_good_buying
  FROM buying
  GROUP BY id_good,product_name
) t2
on t1.id_good=t2.id_good
and t1.product_name=t2.product_name
LEFT JOIN
(
  SELECT id_good,product_name,SUM(`quantity_order`) sum_quantity_order ,SUM(`summ_good_order`) s_summ_good_order
  FROM selling
  GROUP BY id_good,product_name
) t3
on t1.id_good=t3.id_good
and t1.product_name=t3.product_name