Re: Summing & Grouping in a Hierarchical Structure

<SNIP>

Hello Don,

Perhaps I am missing something about what your constraints are, or what you're trying to achieve, but is there any reason you could not use a series of joined tables indicating parent-child relationships?  The following example follows that in your previous posts.  Note that this approach (as given) will not work if branches stemming from the same node are different lengths.  That is, if you have costs associated with "Transportation.Bicycle.Gear", you could not also have a category "Transportation.Bicycle.Gear.Chain_ring".  (To add the latter category, you'd have to put costs from the former under something like "Transportation.Bicycle.Gear.General" -- or modify the approach.)  However, lengthening the "Alcohol" branches, e.g., by tacking on a level5 table would be easy.  Notice that level3 and level4 are not true look-up tables, since they may contain duplicate cat values.

If I'm off base, by all means specify just how.

Regards,

Bryan

--------------------------------------------------

CREATE TABLE level1 (

  cat   text  PRIMARY KEY

);

CREATE TABLE level2 (

   cat   text   PRIMARY KEY,

   parent   text   REFERENCES level1(cat)

);

CREATE TABLE level3 (

   cat   text,

   parent   text   REFERENCES level2(cat),

   cost   numeric(6,2)

);

CREATE TABLE level4 (

   cat   text,

   parent   text,

   cost   numeric(6,2)

);

INSERT INTO level1

  VALUES ('Transportation'),

         ('Groceries');

INSERT INTO level2

  VALUES ('Auto', 'Transportation'),

         ('Bicycle', 'Transportation'),

         ('Fares', 'Transportation'),

         ('Food', 'Groceries'),

         ('Beverages', 'Groceries');

INSERT INTO level3

  VALUES ('Fuel', 'Auto', 50.00),

         ('Maintenance', 'Auto', 30.00),

         ('Fuel', 'Auto', 25.00), 

         ('Gear', 'Bicycle', 40.00),

         ('Gear', 'Bicycle', 20.00),

         ('Bus', 'Fares', 10.00),

         ('Train', 'Fares', 5.00),

         ('Beverages', 'Food', 30.00),

         ('Fruit_Veg', 'Food', 40.00),

         ('Meat_Fish', 'Food', 80.00),

         ('Grains_Cereals', 'Food', 30.00), 

         ('Alcohol', 'Beverages', NULL),

         ('Juice', 'Beverages', 45.00), 

         ('Other', 'Beverages', 15.00); 

INSERT INTO level4

  VALUES ('Beer', 'Alcohol', 25.00),

         ('Spirits', 'Alcohol', 10.00),

         ('Wine', 'Alcohol', 50.00);

CREATE VIEW all_cats AS (

SELECT a.cat AS level4,

       b.cat AS level3,

       c.cat AS level2,

       d.cat AS level1,

       CASE WHEN a.cost IS NULL THEN 0

            WHEN a.cost IS NOT NULL THEN a.cost

                 END

       + CASE WHEN b.cost IS NULL THEN 0

              WHEN b.cost IS NOT NULL THEN b.cost

         END AS cost

  FROM level4 a

    FULL JOIN

    level3 b

    ON (a.parent = b.cat)

      FULL JOIN

      level2 c

      ON (b.parent = c.cat)

        FULL JOIN

        level1 d

        ON (c.parent = d.cat)

  ORDER BY level1, level2, level3, level4

);

SELECT * FROM all_cats;

     level4  |     level3     |  level2   |     level1     | cost  

    ---------+----------------+-----------+----------------+-------

     Beer    | Alcohol        | Beverages | Groceries      | 25.00

     Spirits | Alcohol        | Beverages | Groceries      | 10.00

     Wine    | Alcohol        | Beverages | Groceries      | 50.00

             | Juice          | Beverages | Groceries      | 45.00

             | Other          | Beverages | Groceries      | 15.00

             | Beverages      | Food      | Groceries      | 30.00

             | Fruit_Veg      | Food      | Groceries      | 40.00

             | Grains_Cereals | Food      | Groceries      | 30.00

             | Meat_Fish      | Food      | Groceries      | 80.00

             | Fuel           | Auto      | Transportation | 50.00

             | Fuel           | Auto      | Transportation | 25.00

             | Maintenance    | Auto      | Transportation | 30.00

             | Gear           | Bicycle   | Transportation | 20.00

             | Gear           | Bicycle   | Transportation | 40.00

             | Bus            | Fares     | Transportation | 10.00

             | Train          | Fares     | Transportation |  5.00

    (16 rows)

SELECT level1,

       count(cost) AS num_branches,

       sum(cost) AS total_cost 

  FROM all_cats

  GROUP BY level1

  ORDER BY level1;

         level1     | num_branches | total_cost 

    ----------------+--------------+------------

     Groceries      |            9 |     325.00

     Transportation |            7 |     180.00

    (2 rows)