Stuck Up In My Own Category Tree

Hi all,

Note: I'm happy to read howtos, tutorials, archived messages - I just
haven't found anything that addresses this yet. I found a related topic on
the novice list, but my post got no response there. I've been struggling
with this for about a week now and need to figure out a solution. Heck,
this may not even be the best approach to hierarchical structures, but it
sure seemed reasonable when I first read up on the subject. Anyway...

I created a category table like so (I got the idea from a website somewhere
that used it in a different way, and did not discuss much about addressing
what I want to accomplish):
cat_id(serial) | cat_name(varchar) | parent_id(int) |
lineage(varchar) | deep(int)
1 root_cat_a Null
1 1
2 sub_cat_1 1
1-2 2
3 sub_sub_cat_a 2
1-2-3 3

I use this to categorize transactions, and use the most appropriate
subcategory for any given transation item in a table called trans_details.
I can easily show transaction amounts by sub-category (SELECT cat_name,
sum(amount) AS "amount" FROM category, trans_details WHERE category_cat_id =
trans_details.cat_id):

cat_name | amount
Transportation: Auto: Fuel | $100
Transportation: Auto: Maint | $150
Transportation: Fares: Bus | $40

but what I cannot figure out is how to create a summary where I show
cat_name | amount
Transportation: Auto | $250

or, what I *really* want:
cat_name | amount
Transportation | $290

Can anyone help me work through this? Frankly, I'm not even sure where to
begin to solve the problem. I have been trying the WITH RECURSIVE feature,
but I do not understand very well how to apply it. The example query I have
brings up an empty result set and I don't have a clue how I could modify it
to make it work. I'm not even sure it's the best method, but it seems like
a reasonable approach. I thought about using regexp to try and match the
initial part of the lineage to the category_id of the parents, something
like:
WHERE c1.category_id = regexp_matches(c2.lineage, 'nnn-'), but lineage is a
text type column, rather than an int, and would need to be cast.

One of the problems I encounter is that a root category with no
sub-categories (naturally) won't show up in the category_id = parent_id
matches, since such a category has no children.

I found an e-mail from an old thread on this topic on the novice list. The
author created a very similar table to mine, but talks more about how to
select the child categories, not the root. And, frankly, his example sql
statements did not bring up the results I would expect. The issue seems to
be somewhat common - I just don't yet have the experience to understand it
well yet. :-)

id info parent_id level node_id
1 Name1 Null 1 1
2 Name2 1 2 2
3 Name3 2 3 3
4 Name4 3 4 4
5 Name5 4 5 5
6 Name5 1 2 6
7 Name6 6 3 7
8 Name7 1 2 8

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