Recursive CTE listing all ancestors as columns - sql

Question

I found many examples that show recursive CTEs that will list the path as a concatenated string and the depth of the level. For example:
CREATE TABLE #Test
(ID varchar(20),
ParentID varchar(20)
)
INSERT INTO #Test values ('100000','HEAD');
INSERT INTO #Test values ('100100','100000');
INSERT INTO #Test values ('100200','100100');
INSERT INTO #Test values ('100300','100200');
INSERT INTO #Test values ('100400','100300');
;WITH CTE AS
(
SELECT ID, ParentID, cast(ID as varchar(100)) as path, 0 AS Level
FROM #Test
WHERE ParentID = 'HEAD'
UNION ALL
SELECT t.Id,t.ParentID, cast(cte.path +'>'+ t.ID as varchar(100)), Level + 1
FROM #Test t
INNER JOIN CTE ON t.ParentID = CTE.ID
)
SELECT * FROM CTE
DROP table #Test
Is there a way to return each ancestor in each row in a separate column? So instead of the current result:
ID ParentId Path Level
100000 HEAD 100000 0
100100 100000 100000>100100 1
100200 100100 100000>100100>100200 2
100300 100200 100000>100100>100200>100300 3
100400 100300 100000>100100>100200>100300>100400 4
It would be:
Id Parent L0 L1 L2 L3 L4
100000 HEAD 100000 Null Null Null Null
100100 100000 100000 100100 Null Null Null
100200 100100 100000 100100 100200 Null Null
100300 100200 100000 100100 100200 100300 Null
100400 100300 100000 100100 100200 100300 100400
Assumption is that I know the max level of depth, in this example the max level is 5. SQL Server ver. 12.0, and DB Compatibility is at 120.

Answer 1

If you have a known or maximum number of levels, consider a bit of JSON.
If not 2016+ ... there is a similar XML approach.
Example
;WITH CTE AS
(
SELECT ID, ParentID, cast(ID as varchar(100)) as path, 0 AS Level
FROM #Test
WHERE ParentID = 'HEAD'
UNION ALL
SELECT t.Id,t.ParentID, cast(cte.path +'>'+ t.ID as varchar(100)), Level + 1
FROM #Test t
INNER JOIN CTE ON t.ParentID = CTE.ID
)
SELECT A.ID
,A.ParentID
,B.*
,A.Level
FROM CTE A
Cross Apply (
Select L0 = trim(JSON_VALUE(S,'$[0]'))
,L1 = trim(JSON_VALUE(S,'$[1]'))
,L2 = trim(JSON_VALUE(S,'$[2]'))
,L3 = trim(JSON_VALUE(S,'$[3]'))
,L4 = trim(JSON_VALUE(S,'$[4]'))
,L5 = trim(JSON_VALUE(S,'$[5]'))
From ( values ( '["'+replace(path,'>','","')+'"]' ) ) A(S)
) B
Returns
UPDATE: The XML Approach
;WITH CTE AS
(
SELECT ID, ParentID, cast(ID as varchar(100)) as path, 0 AS Level
FROM #Test
WHERE ParentID = 'HEAD'
UNION ALL
SELECT t.Id,t.ParentID, cast(cte.path +'>'+ t.ID as varchar(100)), Level + 1
FROM #Test t
INNER JOIN CTE ON t.ParentID = CTE.ID
)
SELECT A.ID
,A.ParentID
,B.*
,A.Level
FROM CTE A
Cross Apply (
Select L0 = xDim.value('/x[1]','varchar(50)')
,L1 = xDim.value('/x[2]','varchar(50)')
,L2 = xDim.value('/x[3]','varchar(50)')
,L3 = xDim.value('/x[4]','varchar(50)')
,L4 = xDim.value('/x[5]','varchar(50)')
,L5 = xDim.value('/x[6]','varchar(50)')
From (Select Cast('<x>' + replace(Path,'>','</x><x>')+'</x>' as xml) as xDim) as A
) B

Answer 2

as everyone mentioned you need to know number of levels you have , but here is the implementation with PIVOT:
;WITH CTE AS
(
SELECT ID, ParentID, cast(ID as varchar(100)) as path, 0 AS Level
FROM #Test
WHERE ParentID = 'HEAD'
UNION ALL
SELECT t.Id,t.ParentID, cast(cte.path +'>'+ t.ID as varchar(100)), Level + 1
FROM #Test t
INNER JOIN CTE ON t.ParentID = CTE.ID
)
select
*
from (
Select Id , ParentID,
'L'+ CAST(Row_Number() Over (Partition By ID Order By ID) AS VARCHAR)AS Col,
Split.value
, level
From CTE
Cross apply string_split(path,'>') as Split
) AS tbl
Pivot (Max(value) For Col IN ([L1],[L2],[L3],[L4],[L5])) AS Pvt