Blank rows for every combination

Question

I've got a dimension with this hierarchy of levels A | B | C where all of them are a detail of the previous one.
When I look into the dimension table I get:
A1
A2
A1 B1
A1 B2
A1 B1 C1
A1 B1 C2
etc.
If, in Oracle Answers, I pick up attributes from B and C in the same report, then a record is showed for every combination of B and C with blank attributes for C.
Table B
B1
B2
Table C
C1
C2
C3
The output in Oracle Answers is:
B1 C1
B1 Null
B1 C2
B1 Null
B1 C3
B1 Null
and so on ...
Every row of table B is combined with a row of C and another one with all of its atributtes null.
Any hint?

Answer 1

Nihar
To get the first two rows from each group, you could do this:
Use the ROW_NUMBER() analytic function (see http://download.oracle.com/docs/cd/B19306_01/server.102/b14200/functions137.htm#i86310)
Now, your question isn't clear what you mean by "last" two rows. Last in what order? Whatever it is, you can use the ORDER BY part of the ROW_NUMBER() function to specify the ordering, and reverse it using DESC - for example:
select acn, adate, cost, appl from (
    select acn, adate, cost, appl,
              row_number() over (partition by acn order by adate desc) as rn
    from  acntab
where rn <= 2
order by acn, rnHTH
Regards Nigel