sql recursion: find tree given middle node - tsql

Question

I need to get a tree of related nodes given a certain node, but not necessary top node. I've got a solution using two CTEs, since I am struggling to squeeze it all into one CTE :). Might somebody have a sleek solution to avoid using two CTEs? Here is some code that I was playing with:
DECLARE #temp AS TABLE (ID INT, ParentID INT)
INSERT INTO #temp
SELECT 1 ID, NULL AS ParentID
UNION ALL
SELECT 2, 1
UNION ALL
SELECT 3, 2
UNION ALL
SELECT 4, 3
UNION ALL
SELECT 5, 4
UNION ALL
SELECT 6, NULL
UNION ALL
SELECT 7, 6
UNION ALL
SELECT 8, 7
DECLARE #startNode INT = 4
;WITH TheTree (ID,ParentID)
AS (
SELECT ID, ParentID
FROM #temp
WHERE ID = #startNode
UNION ALL
SELECT t.id, t.ParentID
FROM #temp t
JOIN TheTree tr ON t.ParentID = tr.ID
)
SELECT * FROM TheTree
;WITH Up(ID,ParentID)
AS (
SELECT t.id, t.ParentID
FROM #temp t
WHERE t.ID = #startNode
UNION ALL
SELECT t.id, t.ParentID
FROM #temp t
JOIN Up c ON t.id = c.ParentID
)
--SELECT * FROM Up
,TheTree (ID,ParentID)
AS (
SELECT ID, ParentID
FROM Up
WHERE ParentID is null
UNION ALL
SELECT t.id, t.ParentID
FROM #temp t
JOIN TheTree tr ON t.ParentID = tr.ID
)
SELECT * FROM TheTree
thanks

Answer 1

Meh. This avoids using two CTEs, but the result is a brute force kludge that hardly qualifies as "sleek" as it won’t be efficient if your table is at all sizeable. It will:
Recursively build all possible hierarchies
As you build them, flag the target NodeId as you find it
Return only the targeted tree
I threw in column “TreeNumber” on the off-chance the TargetId appears in multiple hierarchies, or if you’d ever have multiple values to check in one pass. “Depth” was added to make the output a bit more legible.
A more complex solution like #John’s might do, and more and subtler tricks could be done with more detailed table sturctures.
DECLARE #startNode INT = 4
;WITH cteAllTrees (TreeNumber, Depth, ID, ParentID, ContainsTarget)
AS (
SELECT
row_number() over (order by ID) TreeNumber
,1
,ID
,ParentID
,case
when ID = #startNode then 1
else 0
end ContainsTarget
FROM #temp
WHERE ParentId is null
UNION ALL
SELECT
tr.TreeNumber
,tr.Depth + 1
,t.id
,t.ParentID
,case
when tr.ContainsTarget = 1 then 1
when t.ID = #startNode then 1
else 0
end ContainsTarget
FROM #temp t
INNER JOIN cteAllTrees tr
ON t.ParentID = tr.ID
)
SELECT
TreeNumber
,Depth
,ID
,ParentId
from cteAllTrees
where TreeNumber in (select TreeNumber from cteAllTrees where ContainsTarget = 1)
order by
TreeNumber
,Depth
,ID

Answer 2

Here is a technique where you can select the entire hierarchy, a specific node with all its children, and even a filtered list and how they roll.
Note: See the comments next to the DECLAREs
Declare #YourTable table (id int,pt int,name varchar(50))
Insert into #YourTable values
(1,null,'1'),(2,1,'2'),(3,1,'3'),(4,2,'4'),(5,2,'5'),(6,3,'6'),(7,null,'7'),(8,7,'8')
Declare #Top int = null --<< Sets top of Hier Try 2
Declare #Nest varchar(25) = '|-----' --<< Optional: Added for readability
Declare #Filter varchar(25) = '' --<< Empty for All or try 4,6
;with cteP as (
Select Seq = cast(1000+Row_Number() over (Order by name) as varchar(500))
,ID
,pt
,Lvl=1
,name
From #YourTable
Where IsNull(#Top,-1) = case when #Top is null then isnull(pt,-1) else ID end
Union All
Select Seq = cast(concat(p.Seq,'.',1000+Row_Number() over (Order by r.name)) as varchar(500))
,r.ID
,r.pt
,p.Lvl+1
,r.name
From #YourTable r
Join cteP p on r.pt = p.ID)
,cteR1 as (Select *,R1=Row_Number() over (Order By Seq) From cteP)
,cteR2 as (Select A.Seq,A.ID,R2=Max(B.R1) From cteR1 A Join cteR1 B on (B.Seq like A.Seq+'%') Group By A.Seq,A.ID )
Select Distinct
A.R1
,B.R2
,A.ID
,A.pt
,A.Lvl
,name = Replicate(#Nest,A.Lvl-1) + A.name
From cteR1 A
Join cteR2 B on A.ID=B.ID
Join (Select R1 From cteR1 where IIF(#Filter='',1,0)+CharIndex(concat(',',ID,','),concat(',',#Filter+','))>0) F on F.R1 between A.R1 and B.R2
Order By A.R1