join within recursive with adjacency - sql

Question

I have something like this:
CREATE TABLE categories (
id varchar(250) PRIMARY KEY,
name varchar(250) NOT NULL,
parentid varchar(250)
);
CREATE TABLE products (
id varchar(250) PRIMARY KEY,
name varchar(250) NOT NULL,
price double precision,
category varchar(250) NOT NULL
);
INSERT INTO categories VALUES ('1', 'Rack', '');
INSERT INTO categories VALUES ('2', 'Women', '1');
INSERT INTO categories VALUES ('3', 'Shorts', '2');
INSERT INTO products VALUES ('1', 'Jean', 2.99, '3');
INSERT INTO products VALUES ('2', 'Inflatable Boat', 5.99, '1');
Now, if I wanted to see the total price of products for each category, I could do something like this:
SELECT
categories.name,
SUM(products.price) AS CATPRICE
FROM
categories,
products
WHERE products.category = categories.id
GROUP BY categories.name
;
Which produces output:
name | catprice
--------+----------
Rack | 5.99
Shorts | 2.99
(2 rows)
But notice that "Shorts" is an ancestor of "Rack". I want a query that will produce output like this:
name | catprice
--------+----------
Rack | 8.98
(1 row)
So that all product prices are added together under the root category. There are multiple root categories in the category table; only one has been shown for simplicity.
This is what I have thus far:
-- "nodes_cte" is the virtual table that is being created as the recursion continues
-- The contents of the ()s are the columns that are being built
WITH RECURSIVE nodes_cte(name, id, parentid, depth, path) AS (
-- Base case?
SELECT tn.name, tn.id, tn.parentid, 1::INT AS depth, tn.id::TEXT AS path FROM categories AS tn, products AS tn2
LEFT OUTER JOIN categories ON tn2.CATEGORY = categories.ID
WHERE tn.parentid IS NULL
UNION ALL
-- nth case
SELECT c.name, c.id, c.parentid, p.depth + 1 AS depth, (p.path || '->' || c.id::TEXT) FROM nodes_cte AS p, categories AS c, products AS c2
LEFT OUTER JOIN categories ON c2.CATEGORY = categories.ID
WHERE c.parentid = p.id
)
SELECT * FROM nodes_cte AS n ORDER BY n.id ASC;
I have no clue what I've done wrong. The above query returns zero results.

Answer 1

Your recursive query is off by a little. Give this a try:
EDIT -- To make this work with the SUM, use this:
WITH RECURSIVE nodes_cte(name, id, id2, parentid, price) AS (
-- Base case?
SELECT c.name,
c.id,
c.id id2,
c.parentid,
p.price
FROM categories c
LEFT JOIN products p on c.id = p.category
WHERE c.parentid = ''
UNION ALL
-- nth case
SELECT n.name,
n.id,
c.id id2,
c.parentid,
p.price
FROM nodes_cte n
JOIN categories c on n.id2 = c.parentid
LEFT JOIN products p on c.id = p.category
)
SELECT id, name, SUM(price) FROM nodes_cte GROUP BY id, name
And here is the Fiddle: http://sqlfiddle.com/#!1/7ac6d/19
Good luck.