Question

I have a table that store recursive records through two fields: ID and PARENTID.

I have a functionality that can associate a parent to an element of the tree. When I select the elements that can be “parent” of myself I shall obviously exclude from the resulting list all the elements which, directly or indirectly, depends on me but also the elements from which I already depend.

Let’s make an example. Given the following sample hierarchy:

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

If I would like to find the elements that can be parent of element with ID = 4 I shall consider only elements 5 - 3 - 6 because they do not have any relation with the actual structure.

How can I get those elements with a CTE query?

Answer 1

Select *
into #tmp
From Tree2

;WITH Rollups AS (
    SELECT ID, Parent_Id
    FROM tree2 where ID=4
    UNION ALL
    SELECT parent.Id, parent.Parent_Id
    FROM tree2 parent 
    INNER JOIN Rollups child ON child.Id = parent.Parent_Id
)
Delete #tmp from Rollups where #tmp.ID=Rollups.ID

;WITH Rollups AS (
    SELECT ID, Parent_Id
    FROM tree2 where ID=4
    UNION ALL
    SELECT parent.Id, parent.Parent_Id
    FROM tree2 parent 
    INNER JOIN Rollups child ON child.Parent_Id = parent.Id
)
Delete #tmp from Rollups where #tmp.ID=Rollups.ID

Select * from #tmp
Drop Table #tmp