CTE to return all items in hierarchy - sql-server

Question

I have a table with a recursive hierarchy (i.e. ID, ParentID). For any item in this hierachy, I want to be able to bring back a list of everything UP AND DOWN the hierarchy along with the level for each row. Assume that a parent can only ever have a single child.
Take for example the following:
ID ParentID
--------------
1 NULL
2 1
3 2
4 NULL
5 4
6 5
Given ID 1, 2, or 3, I want to return:
ID ParentID Level
-----------------------
1 NULL 1
2 1 2
3 2 3
I've done this before, but I can't remember how. I know the solution involves a CTE, I just can't get it right! Any help is appreciated.

Answer 1

;with cte as
(
select *, 1 as level from #t where id = #yourid
union all
select t.*, level - 1
from cte
inner join #t t on cte.parent = t.id
),
cte2 as
(
select * from cte
union all
select t.*, level+1
from cte2
inner join #t t on cte2.id = t.parent
)
select id,parent, ROW_NUMBER() over (order by level) level
from ( select distinct id, parent, level from cte2) v

Answer 2

The most barebones version of the CTE query I could come up with is:
WITH Ancestry (AncestorID, DescendantID)
AS
(
SELECT
ParentID, ID
FROM
dbo.Location
WHERE
ParentID IS NOT NULL
UNION ALL
SELECT
P.AncestorID, C.ID
FROM
dbo.Location C
JOIN
Ancestry P on C.ParentID = P.DescendantID
)
SELECT * FROM Ancestry
The result is a list of all Ancestor/Descendant relationships that exist in the table.
The final "SELECT * FROM Ancestry" can be replaced with something more complex to filter, order, etc.
To include reflexive relationships, the query can be modified by adding two lines to the final SELECT statement:
SELECT * FROM Ancestry
UNION
SELECT ID, ID FROM dbo.Location

Answer 3

;WITH Recursive_CTE AS (
SELECT
child.ExecutiveId,
CAST(child.ExecutiveName as varchar(100)) BusinessUnit,
CAST(NULL as bigint) ParentUnitID,
CAST(NULL as varchar(100)) ParentUnit,
CAST('' as varchar(100)) LVL,
CAST(child.ExecutiveId as varchar(100)) Hierarchy,
1 AS RecursionLevel
FROM Sales_Executive_level child
WHERE ExecutiveId = 4000 --your Id which you want to get all parent node
UNION ALL
SELECT
child.ExecutiveId,
CAST(LVL + child.ExecutiveName as varchar(100)) AS BusinessUnit,
child.ParentExecutiveID,
parent.BusinessUnit ParentUnit,
CAST('' + LVL as varchar(100)) AS LVL,
CAST(Hierarchy + ':' + CAST(child.ExecutiveId as varchar(100)) as varchar(100)) Hierarchy,
RecursionLevel + 1 AS RecursionLevel
FROM Recursive_CTE parent
INNER JOIN Sales_Executive_level child ON child.ParentExecutiveID = parent.ExecutiveId
)
SELECT * FROM Recursive_CTE ORDER BY Hierarchy
OPTION (MAXRECURSION 300);