Например так мы отберём детей А и В: select child_id from hierarchy start with parent_id is null connect by prior parent_id = child_id and parent_id in ('Parent_A', 'Parent_B')
Например так мы отберём детей А и В: select child_id from hierarchy start with parent_id is null connect by prior parent_id = child_id and parent_id in ('Parent_A', 'Parent_B')