Create a view to shows data from multiple rows in a single column

Question

Hi all - this is probably posted in the wrong forum but I couldn't find which was the correct one.
I am almost a complete novice at sql but I have a need to create a view which can be developed at 10g (which runs efficiently as the volumes are likely to be high) which will do the following.
Original table with columns Parent_code, Child_code
Parent_Code Child_Code
1000 2000
1000 3000
1000 4000
2000 3000
2000 5000
(note Parents can have multiple children and a child can have multiple parents!)
What I need to end up with in my view is the following
Child_Code Parent_List
2000 '1000 (3)'
3000 '1000 (3), 2000 (2)'
4000 '1000 (3)'
5000 '2000 (2)'
Note the number in parantheses is the number of children that the parent has - ie in the original table parent 1000 has 3 rows (one for each child)
This view is then to be used as a look up (on child code) for a business objects report.
Is there anyone who could PLEASE, PLEASE help me fairly quickly on this as I have very little time to find a solution?

Answer 1

Hi,
You can test these ones :
select child_code
     , ltrim(sys_connect_by_path(parent_info,', '), ', ') as parent_list
from (
  select child_code
       , to_char(parent_code) ||
         ' (' ||
         count(*) over(partition by parent_code) ||
         ')' as parent_info
       , row_number() over(partition by child_code order by parent_code) rn
  from your_table
where connect_by_isleaf = 1
connect by prior rn = rn-1
       and prior child_code = child_code
start with rn = 1
select child_code,
       rtrim(
         extract(
           xmlagg(xmlelement("e",parent_info||', ') order by parent_info)
         , '//text()'
       ) as parent_list
from (
  select child_code,
         to_char(parent_code) ||
         ' (' ||
         count(*) over(partition by parent_code) ||
         ')' as parent_info
  from your_table
group by child_code
;What you need is called "string aggregation".
See here for various techniques, including the two above : http://www.oracle-base.com/articles/misc/StringAggregationTechniques.php