SQL - Query to identify the parentid in a hierarchy with some conditions - sql

Question

I have a table in SQL azure database with a hierarchy of parents and i want to identify in the total hierarchy of the parents the parent id for each item that meets some conditions.
As an example this could be a great example
categoryId parentId Typeid
1 null 1
2 1 2
3 2 3
4 3 4
5 3 4
6 null 5
7 6 1
8 7 2
9 8 3
10 9 4
11 9 4
And I want to find for each categoryID the ParentId in the hierarchy that the type is 1 and if this category is the type 1 put the same category, in order to receive something like this.
categoryId parentId Typeid ParentSearch
1 null 1 1
2 1 2 1
3 2 3 1
4 3 4 1
5 3 4 1
6 null 5 null
7 6 1 7
8 7 2 7
9 8 3 7
10 9 4 7
11 9 4 7
As you can see all the categories from 1 to 5 the parent with type 1 is the category 1
and for the categories from 6 to 11, the 6 need to be null and the rest the parent is 7.
It could be possible?
Maybe creating a path or something. i have done doing several left joins at leves and it is fine but i dont want to create 500leves in order to be sure that we never have 500 levels childs.
Thanks and regards!

Answer 1

A recursive CTE is your friend:
WITH parents AS
(SELECT categoryid, parentid, typeid
, CASE WHEN typeid = 1 THEN categoryid ELSE NULL END AS parentsearch
FROM mytable
WHERE parentid IS NULL
UNION ALL
SELECT c.categoryid, c.parentid, c.typeid
, coalesce(p.parentsearch, CASE WHEN c.typeid = 1 THEN c.categoryid ELSE null END)
FROM mytable AS c
JOIN parents AS p ON c.parentid = p.categoryid)
SELECT * FROM parents ORDER BY categoryid;
categoryid parentid typeid parentsearch
---------- ---------- ---------- ------------
1 (null) 1 1
2 1 2 1
3 2 3 1
4 3 4 1
5 3 4 1
6 (null) 5 (null)
7 6 1 7
8 7 2 7
9 8 3 7
10 9 4 7
11 9 4 7
Sql Server db<>fiddle example.

Answer 2

Another solution that uses a recursive CTE.
But this one seeds from the childs.
WITH RCTE AS
(
SELECT t.categoryId, t.parentId, t.typeId,
0 as lvl,
t.categoryId as nextCategoryId,
t.parentId as nextParentId,
t.typeId as nextTypeId
FROM CategoryRelations t
UNION ALL
SELECT c.categoryId, c.parentId, c.typeId,
c.lvl + 1,
t.categoryId,
t.parentId,
t.typeId
FROM RCTE c
JOIN CategoryRelations t ON t.categoryId = c.nextParentId
WHERE c.typeId != 1
)
SELECT
c.categoryId,
c.parentId,
c.typeId,
(case when c.nextTypeId = 1 then c.nextCategoryId end) as ParentSearch
FROM RCTE c
WHERE (c.nextTypeId = 1 or c.parentId is null)
ORDER BY categoryId;
A test on rextester here