Check hierarchically for parent number - sql-server

Question

Table that I am using is CADIGR, and column DIGR_KEY1 is always a parent number (DIGR_KEY of the parent) in the row.
I must update CADIGR DIGR_KEY1 (parent number), but first I must check that I am not updating child with one of theirs parent.
I really don't have idea how to do this? Child can have a lot of parents, so check must be done on the whole tree up to the root (where DIGR_KEY1 IS NULL).
Only if the number does not exist as parent number of that child's tree, update is possible.
CREATE TABLE CADIGR
(
DIGR_KEY INT,
DIGR_KEY1 INT
)
INSERT INTO CADIGR (DIGR_KEY, DIGR_KEY1)
VALUES
(1, NULL),
(2,1),
(3,1),
(4,1),
(11,4),
(12,4),
(13,4),
(5,2),
(6,2),
(5,2),
(6,2),
(7,5),
(8,5),
(9,5),
(10,5),
(14,3),
(15,3)

Answer 1

You can use a recursive query like this, can use level to perform operations on each group of childs.
WITH Rec as
(
SELECT digr_key, digr_key1, 1 AS level
FROM CADIGR
WHERE digr_key1 is null
UNION ALL
SELECT c.digr_key, c.digr_key1, level = level + 1
FROM CADIGR c
INNER JOIN rec
ON c.digr_key1 = rec.digr_key
)
SELECT *
FROM Rec;
GO
digr_key | digr_key1 | level
-------: | --------: | ----:
1 | null | 1
2 | 1 | 2
3 | 1 | 2
4 | 1 | 2
11 | 4 | 3
12 | 4 | 3
13 | 4 | 3
14 | 3 | 3
15 | 3 | 3
5 | 2 | 3
6 | 2 | 3
5 | 2 | 3
6 | 2 | 3
7 | 5 | 4
8 | 5 | 4
9 | 5 | 4
10 | 5 | 4
7 | 5 | 4
8 | 5 | 4
9 | 5 | 4
10 | 5 | 4
dbfiddle here
Avoiding duplicated records
WITH DistData as
(
SELECT DISTINCT digr_key, digr_key1
FROM CADIGR
)
, Rec as
(
SELECT digr_key, digr_key1, 1 AS level
FROM DistData
WHERE digr_key1 is null
UNION ALL
SELECT c.digr_key, c.digr_key1, level = level + 1
FROM DistData c
INNER JOIN rec
ON c.digr_key1 = rec.digr_key
)
SELECT *
FROM Rec;
GO
digr_key | digr_key1 | level
-------: | --------: | ----:
1 | null | 1
2 | 1 | 2
3 | 1 | 2
4 | 1 | 2
11 | 4 | 3
12 | 4 | 3
13 | 4 | 3
14 | 3 | 3
15 | 3 | 3
5 | 2 | 3
6 | 2 | 3
7 | 5 | 4
8 | 5 | 4
9 | 5 | 4
10 | 5 | 4
dbfiddle here