Find level of categories in a hierarchy - sql

Question

I have a script to find the hierarchy of a list of categories. However I would need to know the depth of the level to find all corresponding categories. So my question is there a better way to rewrite the code so that it can drill down to the lowest level without my need to specify how deep to go. As the example below, I had to know that the category level goes to 5 level deep to find all categories.
WITH rCTE AS
(
SELECT
*,
0 AS Level
FROM dbo.inv_category ic
WHERE ic.Primary_org_id = 56392
UNION ALL
SELECT
t.*,
r.Level + 1 AS Level
FROM dbo.inv_category t
INNER JOIN rCTE r ON t.Parent_id = r.Category_id
)
SELECT DISTINCT
c1.Parent_id, c1.Category_id, c1.Category,
c2.Category, c2.Category_id, c2.Parent_id,
c3.Category, c3.Category_id, c3.Parent_id,
c4.Category, c4.Category_id, c4.Parent_id,
c5.Category, c5.Category_id, c5.Parent_id
FROM
rCTE c1
LEFT OUTER JOIN
rCTE c2 ON c1.Category_id = c2.Parent_id
LEFT OUTER JOIN
rCTE c3 ON c2.Category_id = c3.Parent_id
LEFT OUTER JOIN
rCTE c4 ON c3.Category_id = c4.Parent_id
LEFT OUTER JOIN
rCTE c5 ON c4.Category_id = c5.Parent_id
WHERE
c1.Parent_id = 0
ORDER BY
c1.Category, c2.Category

Answer 1

Your problem is that you want the parent categories in different columns, which makes the task more complicated that it could be.
One option to shorten the query and avoid multiple joins uses conditional aggregation:
with rcte as (...)
select
max(case when level = 0 then parent_id end) parent_id_0,
max(case when level = 0 then category_id end) category_id_0,
max(case when level = 0 then category end) category_0,
max(case when level = 1 then parent_id end) parent_id_1,
max(case when level = 1 then category_id end) category_id_1,
max(case when level = 1 then category end) category_1,
...
from rcte
You can add more triplets of conditional expression to manage as many maximum levels as needed; when the actual hierarchy of the product exhausts, the following columns will come out empty.
Another option is string aggregation. This generates a unique column for each original column, with all values concatenated in the order in which they appear in the hierarchy:
with rcte as (...)
select
string_agg(parent_id, ' > ') within group(order by level) parent_ids,
string_agg(category_id_id, ' > ') within group(order by level) category_ids,
string_agg(category, ' > ') within group(order by level) categories
from rcte