сума цена на децата в друга таблица mysql

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select ancestor_id as userid, sum(b.price) as total
from webineh_prefix_nodes_paths_tmp a 
join webineh_prefix_nodes_tmp b 
on b.userid = a.descendant_id
where a.ancestor_id in (select userid from webineh_prefix_nodes_tmp where parent = 1)
group by ancestor_id

Демонстрация на SQLFiddle

Редактирано

select ancestor_id as userid, sum(b.price) as total
from webineh_prefix_nodes_paths_tmp a 
join webineh_prefix_nodes_tmp b 
on b.userid = a.descendant_id
inner join webineh_prefix_nodes_tmp c
on a.ancestor_id = c.userid
and c.parent = 1
group by ancestor_id

Демонстрация на SQLFiddle