On Thu, Aug 11, 2011 at 8:39 AM, Don Parris <parri...@gmail.com> wrote:
> 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. > http://old.storytotell.org/blog/2009/08/11/postgresql84-recursive-queries.html That link appears to answer all of your potential questions - how to render the hierarchy, how to find all children of a node, etc.
