SQL Server: How to limit CTE recursion to rows just recursivly added?

Question

Simpler Example

Let\'s try a simpler example, so people can wrap their heads around the concepts, and have a practical example that you can copy&paste into SQL

Answer 1

Well, your answer is not quite that obvious :-)

WITH (NodeChildren) AS
{
   --initialization
   SELECT ParentNodeID, ChildNodeID, 1 AS GenerationsRemoved
   FROM Nodes

This part is called the "anchor" part of the recursive CTE - but it should really only select one or a select few rows from your table - this selects everything!

I guess what you're missing here is simply a suitable WHERE clause:

WITH (NodeChildren) AS
{
   --initialization
   SELECT ParentNodeID, ChildNodeID, 1 AS GenerationsRemoved
   FROM Nodes
   **WHERE ParentNodeID IS NULL**

However, I am afraid your requirement to have not just the "straight" hierarchy, but also the grandparent-child rows, might not be that easy to satisfy.... normally recursive CTE will only ever show one level and its direct subordinates (and that down the hierarchy, of course) - it doesn't usually skip one, two or even more levels.

Hope this helps a bit.

Marc