SQL可以跨多个表计算聚合函数吗？

select owner, sum(num_dogs), sum(num_cats) from
  (select owner, 1 as num_dogs, 0 as num_cats from dogs
   union
   select owner, 0 as num_dogs, 1 as num_cats from cats)
group by owner

我更喜欢这个:

select owner
     , count(dog_name) dogs
     , count(cat_name) cats
  from cats FULL OUTER JOIN dogs ON (cats.owner = dogs.owner)