Update: There is a newer and imho better approach available with Bottom-up hierarchical root path query recipe in oracle .
oracle supports hierarchical queries on tables by the start with and connect by clauses. this usually preassumes that the rows of some table are chained by a value in column dad_id of some row pointing to a value in column son_id in a parent row, where son_id also denotes the primary key in the table. the root rows of the tree being set up that way, furthermore have a dedicated value in column dad_id. for positive, evolving numbers (id’s ;-), one may just choose 0 here. so far, a typical hierarchical query for a (male) family tree may look like this: