Sql recursive query to read hierarchical data

Question

I am trying to come up with a SQL query to read recursive data as below :

ParentId    ChildId
    1          2
    2          3
    3          4
    4          5
    4          6
    8          9

If a ParentId is provided, then the query should return all ChildId s in a recursive manner.

Example : parentId =1 , result = {2, 3, 4, 5, 6}

I found that connect_by_root and connect by prior is what I should be probably using it. However I am not able to get it right.

Database : Oracle and Db2

Answer 1

This should do the trick:

SELECT ChildId, ParentId, LEVEL
   FROM myTable
   CONNECT BY PRIOR ChildId = ParentId;

Answer 2

This did it :

   SELECT childid
   FROM btab
   START WITH parentId = 1
   CONNECT BY PRIOR  childId = parentId;

Thanks to #Bulat & #AngocA, for the pointers