Fascinating article! I have a couple of naive questions about the following bit of G code:

Adjacency (NodeID, ParentID) as -- Adjacency Query

(select 0, ID, ParentID

from dbo.HierarchyHybrid

where ID = @NodeID_in

andexists

(select*

from dbo.HierarchyHybrid h2

where h2.TopParentID = HierarchyHybrid.TopParentID

and RangeStart is null)

1. Is it supposed to have the "select 0, " or is that just a typo? It looks like the surrounding code is expecting 2 values there, not 3. If not a typo, I don't understand the "0" part.

2. Why doesn't this work?

Adjacency (NodeID, ParentID) as -- Adjacency Query

(select 0, ID, ParentID

from dbo.HierarchyHybrid

where ID = @NodeID_in

and RangeStart is null)

Thanks, regardless of whether you have time to reply.