Sqlserver CTE how to get first non null value - sql-server

Question

I am trying to use the following query to get a user with his detail and any of his manager or manager's manager id who got a record in UserTag table.
I have got the partial result, but not sure how to get the first non null value. I have show my expected result below.
With Managers AS
(
--initialization
SELECT Id, Email, ManagerID, NULL as UserID
FROM dbo.[User]
WHERE email='user#test.com'
UNION ALL
--recursive execution
SELECT u.Id, u.Email, u.ManagerID, tb2.UserID
FROM dbo.[User] u
INNER JOIN Managers m ON m.ManagerID = u.ID
OUTER apply (select userid from UserTag where userid = m.ManagerID and (TagID=9 or TagName = 'test')) tb2
)
SELECT * FROM Managers
Expected result:
Sample data and expected result:
User table
=========
Id Email ManagerID
--- ----- ---------
11813 userA#test.com 1251
1251 userB#test.com 302
302 userC#test.com 1221
1221 userD#test.com 358
358 userE#test.com 988
988 userE#test.com NULL
100 userA1#test.com 101
101 userB1#test.com 102
102 userC1#test.com 103
103 userD1#test.com 104
104 userF1#test.com NULL
User Tag
Id UserId TagId TagName
1 1221 9 test
2 104 9 test
Expected result
==============
UserId Email TagManagerId
------ ----- ------------
11813 userA#test.com 1221
1251 userB#test.com 1221
302 userC#test.com 1221
Brief description:
I have all users in User table. This is a self referencing table.
I want to get all users whose immediate manager or manager's manager or any manager in his/hierarchy got a record in UserTag table with tagid=9 or tagname='test' as shown here.
Schema db<>fiddle here

Answer 1

Based on your Brief description, I believe that this is an XY Problem
There are solutions to the real need that don't include get first non null value.
What I believe you really need to do is find all the managers that are tagid=9 or tagname='test' and then recursively find all their subordinates. (Run the recursion in the opposite direction to your example query.)
The only complexity I can think of is that such a manager may have a subordinate that also meets those criteria, so I included a condition to avoid recursing them more than once.
WITH
test9_managed_users AS
(
SELECT
u.*,
u.managerid AS closest_test9_manager_id,
0 AS depth
FROM
[user] AS u
INNER JOIN
UserTag AS t
ON t.userid = u.managerid
AND (t.TagID=9 or TagName = 'test')
UNION ALL
SELECT
u.*,
m.closest_test9_manager_id,
m.depth+1
FROM
test9_managed_users AS m
INNER JOIN
[user] AS u
ON u.managerid = m.id
WHERE
-- If a user is themselves a 'test9_manager', don't recurse their children
-- > They would already have been included in the Anchor part of the CTE
NOT EXISTS (
SELECT *
FROM UserTag AS t
WHERE t.userid = m.id
AND (t.TagID=9 or TagName = 'test')
)
)
SELECT
*
FROM
test9_managed_users
ORDER BY
email
Demo with my own test data:
https://dbfiddle.uk/?rdbms=sqlserver_2017&fiddle=5e901a6f7db97362bb27ebacb1d4331c
Demo with your test data:
https://dbfiddle.uk/?rdbms=sqlserver_2017&fiddle=1ab3625ba797d8fc13c49872d1cd5872