User variable not updating in subquery - mysql

Question

I am using a RECURSIVE statement on MariaDB, to get a product category path when I know the product category unique ID, from a self-referencing category table.
This works:
WITH RECURSIVE categories AS (
SELECT * FROM tbl_eav_categories tec2 WHERE tec2.category_id = 1023
UNION
SELECT tec3.* FROM tbl_eav_categories tec3, categories AS c WHERE tec3.category_id = c.parent_category_id
)
SELECT GROUP_CONCAT(CONCAT(category_default_label,' [',category_id,']') ORDER BY category_id ASC SEPARATOR ' >> ') FROM categories
And returns:
Consumables [7] >> Catering Equipment and Supplies [95] >> Tea Bags [1023]
Great.
But now I need to list all category ID's and in the second column, their paths.
I thought this would simply be a matter of doing a SELECT on the primary category table ('tbl_eav_categories') table, and dropping the above query in as a subquery column. Like this:
SELECT
#CatID := category_id AS 'cat_id',
(
WITH RECURSIVE categories AS (
SELECT * FROM tbl_eav_categories tec2 WHERE tec2.category_id = #CatID
UNION
SELECT tec3.* FROM tbl_eav_categories tec3, categories AS c WHERE tec3.category_id = c.parent_category_id
)
SELECT GROUP_CONCAT(CONCAT(category_default_label,' [',category_id,']') ORDER BY category_id ASC SEPARATOR ' >> ') FROM categories
) 'categorypath'
FROM tbl_eav_categories;
However, all I get is:
cat_id categorypath
1 Bearings [1]
2 Bearings [1]
3 Bearings [1]
4 Bearings [1]
5 Bearings [1]
6 Bearings [1]
...
(like this until the bottom of the entire result set).
After some research, I do believe it has something to do with the #CatID variable being evaluated before it gets assigned, but I can't work out how to work around it.
I tried to follow Ben English's guidance here: User variable in MySQL subquery but it baffles me :(
Please help! :)

Answer 1

I believe I have found the answer, by including the entire table scan in the actual CTE:
WITH RECURSIVE category_path (id, title, path) AS
(
SELECT category_id, category_default_label, category_default_label path FROM tbl_eav_categories WHERE parent_category_id IS NULL
UNION ALL
SELECT c.category_id, c.category_default_label, CONCAT(cp.path, ' [',c.parent_category_id, '] >> ', c.category_default_label) FROM category_path cp JOIN tbl_eav_categories c ON cp.id = c.parent_category_id
)
SELECT id,path FROM category_path
ORDER BY path;