Gruppér ved ikke at arbejde med 2 felter sum

Problemet er, at store med id 1 har to tilsvarende poster i store_sub tabel, hvilket betyder, at qty feltet vises to gange for butik 1. Du skal summere de 2 tabeller separat i underforespørgsler og sammenføje de summerede versioner:

select t1.department, t1.sqty, t2.ssubqty
from
  (select department, sum(qty) as sqty from store group by department) t1
left join
  (select s2.department, s1.sum(sub_qty) as ssubqty
   from store_sub s1
   inner join store s2 on s1.parent_id=s2.id
   group by s2.department) t2 on t1.department=t2.department