Get Root parent of child in Hierarchical table

Question

I have a table with hierarchical data in it, the structure goes like this:

ID      ParentId
----   ----------
1       NULL
2       1
3       2
4       2
5       3
6       5

If I pass the node Id I would like to get the top most node Id/details by traversing through all its parents in SQL.

I tried CTE, i somehow cannot get the combination correct. However, i got this working as a function but it is so slow that i had to post this question.

In the above example if I pass 6, i would want to have the top most i.e. 1. By traversing through 6 => 5 => 3 => 2 => [1] (result)

Thanks in advance for your help.

Solution 1

Please try:

declare @id int=6
;WITH parent AS
(
    SELECT id, parentId  from tbl WHERE id = @id
    UNION ALL 
    SELECT t.id, t.parentId FROM parent
    INNER JOIN tbl t ON t.id =  parent.parentid
)

SELECT TOP 1 id FROM  parent
order by id asc

Solution 2

DECLARE @id INT = 6
;WITH parent AS
(
    SELECT id, parentId, 1 AS [level] from tbl WHERE id = @id
    UNION ALL 
    SELECT t.id, t.parentId, [level] + 1 FROM parent
    INNER JOIN tbl t ON t.id =  parent.parentid
)
SELECT TOP 1 id FROM parent ORDER BY [level] DESC

@TechDo's answer assumes the lowest ID will be the parent. If you don't want to rely on this then the above query will sort by the depth.

Solution 3

You can try this query my friend to get all ids:

with tab1(ID,Parent_ID) as
(select * from table1 where id = 6
union all
select t1.* from table1 t1,tab1 
where tab1.Parent_ID = t1.ID)
select ID from tab1;

and this query will give the final result:

with tab1(ID,Parent_ID) as
(select * from table1 where id = 6
union all
select t1.* from table1 t1,tab1 
where tab1.Parent_ID = t1.ID)
select ID from tab1 where parent_id is null;

SQL Fiddle

Solution 4

;WITH CTE
as
(
    Select I.ID,P.Parent_id
    from #temp I 
    join #temp P 
    on P.Id = I.Parent_Id
    where i.ID = 6
    union all
    Select I.ID,P.Parent_id
    from CTE I 
    join #temp P 
    on P.Id = I.Parent_Id
    where p.Parent_Id is not null
)
Select ID,min(parent_id) from CTE group by id;

Solution 5

 WITH CTE_MyTable AS (
    SELECT        Id, ParentId, NULL As RootParent, 1 As Lvl
    FROM            dbo.MyTable
    UNION ALL
    SELECT        a.id, b.ParentId, a.ParentId As RootParent, Lvl + 1
    FROM            CTE_MyTable a INNER JOIN
                                               dbo.MyTable b ON a.ParentId = b.Id
)
, CTE_MyTable_RN AS  (
    SELECT Id, RootParent, ROW_NUMBER() OVER (PARTITION BY Id ORDER BY Lvl DESC) RN
    FROM CTE_MyTable
)

SELECT Id, ISNULL(RootParent, Id) As RootParent
FROM CTE_MyTable_RN
WHERE RN = 1

View more solutions

Comments

[Mathias F]

doesnt this assume that the root id is the lowest id of the tree? What if the root id has a higher id then the oder nodes?

[Mathias F]

This should be the accepted answer. TechDos answer will give the wrong result if the root has higher id (which is a common case)

[Avin Kavish]

Is there a way to extend this to get the root parent id of each id

[Douglas Marttinen]

@AvinKavish if I'm understanding correctly, I think you can create a function with the above query, then use the function in your own query to get the root ID of each ID.