Philippe Lang, 10.07.2009 11:10:
> Hi,
>
> I'm playing with the new "WITH RECURSIVE" feature of 8.4. I'm trying to
> figure out how to use it with trees.
>
> Here is the test code I use:
>
> I'd like to perform a real recursion, and show the tree structure in a
> more appopriate way, like this:
>
> Any idea how to do that? (without trying to sort on the lookup column,
> whose values can be random outside this test)
The manual has a nice hint on this adding up IDs to "generate" a path like column that can be used for sorting.
Try the following:
WITH RECURSIVE parse_tree (depth, id, lookup, parent_id, sort_path) AS
( SELECT 0, parent.id, cast(parent.lookup as text), parent.parent_id, array[0] as sort_path FROM
recursion_sampleparent WHERE parent_id IS NULL UNION ALL SELECT parent.depth + 1, child.id, rpad(' ', depth *
2)|| child.lookup, child.parent_id, parent.sort_path || child.id FROM parse_tree parent JOIN recursion_sample
childon child.parent_id = parent.id
)
select id, lookup
from parse_tree
order by sort_path
;
This will output:
id | lookup
-----+-------- 1 | a1 2 | b11243 | c113645 | c111823 | c112 6 | b12583 | c122845 | c121 9 | b13 10 |
c131
(10 rows)
Thomas
