Ok, I managed to accomplish my goal with the ltree:
test_ltree=> SELECT subltree(path,0,2), sum(trans_amt) FROM testcat GROUP
BY subltree;
subltree | sum
--------------------+--------
TOP.Groceries | 325.00
TOP.Transportation | 180.00
(2 rows)
It took a bit of experimenting with the various functions of ltree, but I
got what I wanted.
What I did was keep the ltree path column in the same table as the
line-item amount, but this requires building the entire path statement in
every row. That's ok for a quick test to figure out how ltree works, but I
think I do need to keep the category structure in a separate table:
Category (category_id, path)
Anyway, thanks for suggesting ltree.
On Fri, Feb 22, 2013 at 7:15 PM, Don Parris <parri...@gmail.com> wrote:
> Hi Misa,
>
> I decided to try out ltree, and have made some progress with it. If I
> understand correctly how to use it, I simply insert the 'path' column into
> my table, using ltree as the data type. That eliminates the need for a
> category table, if I understand correctly. I just need to ensure the
> category path is correct for each line item in the transaction details
> table.
>
> However, I have difficulty figuring out how to sum the amounts as I would
> like:
> test_ltree=> SELECT path, SUM(trans_amt) FROM testcat WHERE path ~
> 'TOP.*{2}' GROUP BY path;
> path | sum
> ------+-----
> (0 rows)
>
>
> This works fine:
> test_ltree=> SELECT path, trans_amt FROM testcat;
> path | trans_amt
> -----------------------------------------+-----------
> TOP.Transportation.Auto.Fuel | 50.00
> TOP.Transportation.Auto.Maintenance | 30.00
> TOP.Transportation.Auto.Fuel | 25.00
> TOP.Transportation.Bicycle.Gear | 40.00
> TOP.Transportation.Bicycle.Gear | 20.00
> TOP.Transportation.Fares.Bus | 10.00
> TOP.Transportation.Fares.Train | 5.00
> TOP.Groceries.Food.Beverages | 30.00
> TOP.Groceries.Food.Fruit_Veggies | 40.00
> TOP.Groceries.Food.Meat_Fish | 80.00
> TOP.Groceries.Food.Grains_Cereals | 30.00
> TOP.Groceries.Beverages.Alcohol.Beer | 25.00
> TOP.Groceries.Beverages.Alcohol.Spirits | 10.00
> TOP.Groceries.Beverages.Alcohol.Wine | 50.00
> TOP.Groceries.Beverages.Juice | 45.00
> TOP.Groceries.Beverages.Other | 15.00
> (16 rows)
>
>
> But I can do that in my sleep with any regular query. This also works
> great (sum the trans_amt column at level 3 (not counting "TOP"):
> test_ltree=> SELECT path, SUM(trans_amt) FROM testcat WHERE path ~
> 'TOP.*{3}' GROUP BY path;
> path | sum
> -------------------------------------+-------
> TOP.Groceries.Beverages.Juice | 45.00
> TOP.Groceries.Beverages.Other | 15.00
> TOP.Groceries.Food.Beverages | 30.00
> TOP.Groceries.Food.Fruit_Veggies | 40.00
> TOP.Groceries.Food.Grains_Cereals | 30.00
> TOP.Groceries.Food.Meat_Fish | 80.00
> TOP.Transportation.Auto.Fuel | 75.00
> TOP.Transportation.Auto.Maintenance | 30.00
> TOP.Transportation.Bicycle.Gear | 60.00
> TOP.Transportation.Fares.Bus | 10.00
> TOP.Transportation.Fares.Train | 5.00
> (11 rows)
>
> So if I want to see:
> TOP.Groceries | 240.00
> TOP.Transportation | 180.00
>
> How do I get this? Can you help?
>
> I am running PostgreSQL 9.1 on Kubuntu 12.10, in case that makes any
> difference.
>
>
>
> On Fri, Feb 22, 2013 at 4:00 AM, Misa Simic <misa.si...@gmail.com> wrote:
>
>> Hi,
>>
>>
>> Have you considered maybe ltree datatype?
>>
>> http://www.postgresql.org/docs/9.1/static/ltree.html
>>
>> I think it solves a lot of problems in topic....
>>
>> Kind regards,
>>
>> Misa
>>
>>
>> On Friday, February 15, 2013, Don Parris wrote:
>>
>>> Hi all,
>>>
>>> I posted to this list some time ago about working with a hierarchical
>>> category structure. I had great difficulty with my problem and gave up
>>> for a time. I recently returned to it and resolved a big part of it. I
>>> have one step left to go, but at least I have solved this part.
>>>
>>> Here is the original thread (or one of them):
>>>
>>> http://www.postgresql.org/message-id/CAJ-7yonw4_qDCp-ZNYwEkR2jdLKeL8nfGc+-TLLSW=rmo1v...@mail.gmail.com
>>>
>>> Here is my recent blog post about how I managed to show my expenses
>>> summed and grouped by a mid-level category:
>>> http://dcparris.net/2013/02/13/hierarchical-categories-rdbms/
>>>
>>>
>>> Specifically, I wanted to sum and group expenses according to
>>> categories, not just at the bottom tier, but at higher tiers, so as to show
>>> more summarized information. A CEO primarily wants to know the sum total
>>> for all the business units, yet have the ability to drill down to more
>>> detailed levels if something is unusually high or low. In my case, I could
>>> see the details, but not the summary. Well now I can summarize by what I
>>> refer to as the 2nd-level categories.
>>>
>>> Anyway, I hope this helps someone, as I have come to appreciate - and I
>>> mean really appreciate - the challenge of working with hierarchical
>>> structures in a 2-dimensional RDBMS. If anyone sees something I should
>>> explain better or in more depth, please let me know.
>>>
>>> Regards,
>>> Don
>>> --
>>> D.C. Parris, FMP, Linux+, ESL Certificate
>>> Minister, Security/FM Coordinator, Free Software Advocate
>>> http://dcparris.net/
>>> <https://www.xing.com/profile/Don_Parris><http://www.linkedin.com/in/dcparris>
>>> GPG Key ID: F5E179BE
>>>
>>
>
>
> --
> D.C. Parris, FMP, Linux+, ESL Certificate
> Minister, Security/FM Coordinator, Free Software Advocate
> http://dcparris.net/
> <https://www.xing.com/profile/Don_Parris><http://www.linkedin.com/in/dcparris>
> GPG Key ID: F5E179BE
>
--
D.C. Parris, FMP, Linux+, ESL Certificate
Minister, Security/FM Coordinator, Free Software Advocate
http://dcparris.net/
<https://www.xing.com/profile/Don_Parris><http://www.linkedin.com/in/dcparris>
GPG Key ID: F5E179BE
