How to return specific row number of a Hierachial query - Oracle
See this article from Oracle why the rownum approach won't work:
http://docs.oracle.com/cd/B19306_01/server.102/b14200/pseudocolumns009.htm

See this article on StackOverflow for the solution:
https://stackoverflow.com/questions/13351318/table-rownum-returns-0-records-if-rownum-is-tested-for-value-greater-than-100

Edit (for those who don't like reading):
- you want to do something like this

select count(*)
from (select rownum r
        from some_table
        order by r)
where r&gt;=101 
and rownum &lt;= 400;