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