SQL select parent-child recursively based on a reference table - sql

Question

I saw many questions related to a recursive query but couldn't find any that shows how to use it based on a reference table.
I have a MasterTable where Id, ParentId columns are establishing the parent/child relation.
I have a SubTable where I have a bunch of Ids which could be a parent Id or child Id.
I would like to retrieve all related records (parent or child, recursively) from the MasterTable based on given SubTable
Current output:
id parentId
----------- -----------
1 NULL
2 1
3 1
4 NULL
5 4
6 5
7 6
Expected output
id parentId
----------- -----------
1 NULL
2 1
3 1
4 NULL
5 4
6 5
7 6
8 9
9 NULL
10 NULL
11 10
13 11
14 10
15 16
16 NULL
Comparison of actual vs expected:
Code:
DECLARE #MasterTable TABLE
(
id INT NOT NULL,
parentId INT NULL
);
DECLARE #SubTable TABLE
(
id INT NOT NULL
);
INSERT INTO #MasterTable (id, parentId)
VALUES (1, NULL), (2, 1), (3, 1), (4, NULL), (5, 4), (6, 5),
(7, 6), (8, 9), (9, NULL), (10, NULL), (11, 10), (12, NULL),
(13, 11), (13, 11), (14, 10), (15, 16), (16, NULL);
INSERT INTO #SubTable (id)
VALUES (1), (2), (3), (4), (6), (5), (7),
(8), -- it does not show
(13), -- it does not show
(15); -- it does not show
/* beside 8,13,15 it should add 9,11,14 and 10,16 */
;WITH cte AS
(
SELECT
mt1.id,
mt1.parentId
FROM
#MasterTable AS mt1
WHERE
mt1.parentId IS NULL
AND EXISTS (SELECT NULL AS empty
FROM #SubTable AS st
WHERE st.Id = mt1.id)
UNION ALL
SELECT
mt2.id,
mt2.parentId
FROM
#MasterTable AS mt2
INNER JOIN
cte AS c1 ON c1.id = mt2.parentId
)
SELECT DISTINCT
c2.id,
c2.parentId
FROM
cte AS c2
ORDER BY
id;

Answer 1

Is the following query suitable for the issue in question?
with
r as(
select
m.*, iif(m.parentid is null, 1, 0) p_flag
from #MasterTable m
join #SubTable s
on s.id = m.id
union all
select
m.*, iif(m.parentid is null, 1, r.p_flag)
from r
join #MasterTable m
on (r.p_flag = 1 and m.parentid = r.id) or
(r.p_flag = 0 and r.parentid = m.id)
)
select distinct
id, parentid
from r
order by id;
Output:
| id | parentid |
+----+----------+
| 1 | NULL |
| 2 | 1 |
| 3 | 1 |
| 4 | NULL |
| 5 | 4 |
| 6 | 5 |
| 7 | 6 |
| 8 | 9 |
| 9 | NULL |
| 10 | NULL |
| 11 | 10 |
| 13 | 11 |
| 14 | 10 |
| 15 | 16 |
| 16 | NULL |
Test it online with rextester.com.

Answer 2

;WITH cte
AS (
SELECT mt1.id,
mt1.parentId
FROM #MasterTable AS mt1
WHERE mt1.parentId IS NULL
UNION ALL
SELECT mt2.id,
mt2.parentId
FROM #MasterTable AS mt2
INNER JOIN cte AS c1
ON c1.id = mt2.parentId
)
SELECT DISTINCT c2.id,
c2.parentId
FROM cte AS c2
where
EXISTS (
SELECT 1 AS empty FROM #SubTable AS st
WHERE ( st.Id = c2.id or st.Id = c2.parentId)
)
or
EXISTS (
SELECT 1 AS empty FROM #MasterTable AS mt
WHERE ( c2.Id = mt.parentId or c2.parentId = mt.parentId)
)
ORDER BY id;

Answer 3

You may try this....
; with cte as(
select distinct mas.id, mas.parentId, iif(mas.parentid is null, 1, 0) PId
from #MasterTable mas inner join #SubTable sub
on sub.id in(mas.id, mas.parentid) ----- create top node having parentid is null
union all
select mas.id, mas.parentId, ct.PId
from cte ct inner join #MasterTable mas
on (ct.PId = 1 and mas.parentid = ct.id) or
(ct.PId = 0 and ct.parentid = mas.id) ----- create child node for correspoding parentid created above
)
select distinct id, parentid from cte order by id
option (MAXRECURSION 100); ---- Add Maxrecursion to prevent the infinite loop
You can find this link for more info on recursive query in SQL link. In this link see Example E or above.