Use of rownum in ORACLE, DB2

Assuming that the table named T,primary key is an ID, then:
1-5000000

SELECT t.*
From T, (SELECT ID, row_number () over (ORDER by id) as num from T) as T1
WHERE t.id = t1.id and T1.num <50000001

50000001-100000000

SELECT t.*
From T, (SELECT ID, row_number () over (ORDER by id) as num from T) as T1
WHERE t.id = t1.id and t1.num between 50000001 and 100000000

etc...

To Oracle, since pseudo-column rownum always counts from 1, it is not valid when rownum takes >1 value, such as SELECT * from xxx where rownum = 2, without results.

How subqueries can be used: Select C.* from (SELECT *, rownum as no from XXX) c where c.no = and results are obtained.

Use of rownum in ORACLE, DB2