Recursive CTE with three tables - sql

Question

I'm using SQL Server 2008 R2 SP1.
I would like to recursively find the first non-null manager for a certain organizational unit by "walking up the tree".
I have one table containing organizational units "ORG", one table containing parents for each org. unit in "ORG", lets call that table "ORG_PARENTS" and one table containing managers for each organizational unit, lets call that table "ORG_MANAGERS".
ORG has a column ORG_ID:
ORG_ID
1
2
3
ORG_PARENTS has two columns.
ORG_ID, ORG_PARENT
1, NULL
2, 1
3, 2
MANAGERS has two columns.
ORG_ID, MANAGER
1, John Doe
2, Jane Doe
3, NULL
I'm trying to create a recursive query that will find the first non-null manager for a certain organizational unit.
Basically if I do a query today for the manager for ORG_ID=3 I will get NULL.
SELECT MANAGER FROM ORG_MANAGERS WHERE ORG_ID = '3'
I want the query to use the ORG_PARENTS table to get the parent for ORG_ID=3, in this case get "2" and repeat the query against the ORG_MANAGERS table with ORG_ID=2 and return in this example "Jane Doe".
In case the query also returns NULL I want to repeat the process with the parent of ORG_ID=2, i.e. ORG_ID=1 and so on.
My CTE attempts so far have failed, one example is this:
WITH BOSS (MANAGER, ORG_ID, ORG_PARENT)
AS
( SELECT m.MANAGER, m.ORG_ID, p.ORG_PARENT
FROM dbo.MANAGERS m INNER JOIN
dbo.ORG_PARENTS p ON p.ORG_ID = m.ORG_ID
UNION ALL
SELECT m1.MANAGER, m1.ORG_ID, b.ORG_PARENT
FROM BOSS b
INNER JOIN dbo.MANAGERS m1 ON m1.ORG_ID = b.ORG_PARENT
)
SELECT * FROM BOSS WHERE ORG_ID = 3
It returns:
Msg 530, Level 16, State 1, Line 4
The statement terminated. The maximum recursion 100 has been exhausted before statement completion.
MANAGER ORG_ID ORG_PARENT
NULL 3 2

Answer 1

You need to keep track of the original ID you start with. Try this:
DECLARE #ORG_PARENTS TABLE (ORG_ID INT, ORG_PARENT INT )
DECLARE #MANAGERS TABLE (ORG_ID INT, MANAGER VARCHAR(100))
INSERT #ORG_PARENTS (ORG_ID, ORG_PARENT)
VALUES (1, NULL)
, (2, 1)
, (3, 2)
INSERT #MANAGERS (ORG_ID, MANAGER)
VALUES (1, 'John Doe')
, (2, 'Jane Doe')
, (3, NULL)
;
WITH BOSS
AS
(
SELECT m.MANAGER, m.ORG_ID AS ORI, m.ORG_ID, p.ORG_PARENT, 1 cnt
FROM #MANAGERS m
INNER JOIN #ORG_PARENTS p
ON p.ORG_ID = m.ORG_ID
UNION ALL
SELECT m1.MANAGER, b.ORI, m1.ORG_ID, OP.ORG_PARENT, cnt +1
FROM BOSS b
INNER JOIN #ORG_PARENTS AS OP
ON OP.ORG_ID = b.ORG_PARENT
INNER JOIN #MANAGERS m1
ON m1.ORG_ID = OP.ORG_ID
)
SELECT *
FROM BOSS
WHERE ORI = 3
Results in:
+----------+-----+--------+------------+-----+
| MANAGER | ORI | ORG_ID | ORG_PARENT | cnt |
+----------+-----+--------+------------+-----+
| NULL | 3 | 3 | 2 | 1 |
| Jane Doe | 3 | 2 | 1 | 2 |
| John Doe | 3 | 1 | NULL | 3 |
+----------+-----+--------+------------+-----+
General tips:
Don't predefine the columns of a CTE; it's not necessary, and makes maintenance annoying.
With recursive CTE, always keep a counter, so you can limit the recursiveness, and you can keep track how deep you are.
edit:
By the way, if you want the first not null manager, you can do for example (there are many ways) this:
SELECT BOSS.*
FROM BOSS
INNER JOIN (
SELECT BOSS.ORI
, MIN(BOSS.cnt) cnt
FROM BOSS
WHERE BOSS.MANAGER IS NOT NULL
GROUP BY BOSS.ORI
) X
ON X.ORI = BOSS.ORI
AND X.cnt = BOSS.cnt
WHERE BOSS.ORI IN (3)