Recursion In Oracle

Solution 1:

WITH    Ancestor(arg1, arg2) AS
        (
        SELECT  p.arg1, p.arg2
        FROM    parent p
        WHERE   arg2 NOT IN
        (
            SELECT  arg1
            FROM    parent
        )

        UNION ALL

        SELECT  p.arg1, a.arg2
        FROM    Ancestor a 
        JOIN    parent p
        ON      p.arg2 = a.arg1
        )
SELECT  *
FROM    Ancestor

Oracle only supports recursive CTE since 11g Release 2.

In earlier versions, use CONNECT BY clause:

SELECT  arg1, CONNECT_BY_ROOT arg2
FROM    parent
START WITH
        arg2 NOT IN
        (
        SELECT  arg1
        FROM    parent
        )
CONNECT BY
        arg2 = PRIOR arg1

Solution 2:

Oracle allows recursive queries. See: http://www.adp-gmbh.ch/ora/sql/connect_by.html

Of course, these usually assume the hierarchical data is all in one table. Splitting it into separate tables makes things complicated.