hierarchy/tree - get all strings to root - sql

Question

Say I have this table T below which defines/stored a tree structure by storing parent/child couples. These values are integers. Say in another table S, I have each ID/value mapped to a string.
So, let's say in S we have:
Table S
ID Name
90 "node 90"
301 "node 301"
etc. (even though the real names are different)
Is it possible to add a computed column here in T which gives for each child node, the textual representation of the path all the way up to the root of the tree in an appended form e.g.
"node 1 > node 2 > node 3" (for child/leaf node 3)
or
"node 10 > node 20" (for child/leaf node 20)
If it's not possible through a computed column, then can I do it with a regular column and a one-time update of that column? I was thinking of some recursive CTE but I cannot get my head around it (for now).
Table T
ParentEventID ChildEventID
90 301
90 302
90 303
90 304
90 305
90 306
90 307
301 401
301 402
302 403
302 404
302 405
302 406
302 407
303 408
304 409
304 410
304 411
304 412
304 413
304 414
305 415
305 416
305 417
305 418
306 419
306 420
306 421
306 422
307 423
307 424
307 425
307 426
307 427
403 501
403 502
403 503
403 504
403 505
404 506
404 507
404 508
404 509
404 510
405 511
405 512
405 513
405 514
405 515
406 516
406 517
406 518
406 519
406 520
407 521
407 522
407 523
407 524
407 525
415 526
415 527
415 528
415 529
415 530
416 531
416 532
416 533
416 534
416 535
417 536
417 537
417 538
417 539
417 540
418 541
418 542
418 543
418 544
418 545
420 546
420 547
420 548
420 549
420 550
421 551
421 552
421 553
421 554
421 555
422 556
422 557
422 558
422 559
422 560

Answer 1

Here's what I came up with:
WITH cte AS (
SELECT * FROM (VALUES
(90, 301),
(90, 302),
(90, 303),
(90, 304),
(90, 305),
(90, 306),
(90, 307),
(301,401),
(301,402),
(302,403),
(302,404),
(302,405),
(302,406),
(302,407),
(303,408),
(304,409),
(304,410),
(304,411),
(304,412),
(304,413),
(304,414),
(305,415),
(305,416),
(305,417),
(305,418),
(306,419),
(306,420),
(306,421),
(306,422),
(307,423),
(307,424),
(307,425),
(307,426),
(307,427),
(403,501),
(403,502),
(403,503),
(403,504),
(403,505),
(404,506),
(404,507),
(404,508),
(404,509),
(404,510),
(405,511),
(405,512),
(405,513),
(405,514),
(405,515),
(406,516),
(406,517),
(406,518),
(406,519),
(406,520),
(407,521),
(407,522),
(407,523),
(407,524),
(407,525),
(415,526),
(415,527),
(415,528),
(415,529),
(415,530),
(416,531),
(416,532),
(416,533),
(416,534),
(416,535),
(417,536),
(417,537),
(417,538),
(417,539),
(417,540),
(418,541),
(418,542),
(418,543),
(418,544),
(418,545),
(420,546),
(420,547),
(420,548),
(420,549),
(420,550),
(421,551),
(421,552),
(421,553),
(421,554),
(421,555),
(422,556),
(422,557),
(422,558),
(422,559),
(422,560)
) AS x(ParentEventID, ChildEventID)
), rcte AS (
SELECT DISTINCT NULL AS [ParentEventID], a.[ParentEventID] AS ChildEventID, CONCAT('/', CAST(a.[ParentEventID] AS NVARCHAR(MAX)), '/') AS h
FROM cte AS a
WHERE NOT EXISTS (
SELECT *
FROM [cte]
WHERE [cte].[ChildEventID] = a.[ParentEventID]
)
UNION ALL
SELECT child.[ParentEventID], child.[ChildEventID], CONCAT(parent.h, [child].[ChildEventID], '/')
FROM [cte] AS child
JOIN rcte AS parent
ON child.[ParentEventID] = [parent].[ChildEventID]
)
SELECT * FROM rcte
The first cte is just a quick way for me to expose your data; the real meat of the solution is in rcte. Note, the h column is immediately convertible to a HierarchyID if that is what you're looking for. Which, by the way, you should be looking for that as that allows for you to answer questions of the type "what are the children of this row?" or "which rows are in this row's lineage?" quite easily (i.e. w/o having to compute the entire hierarchy on the fly).