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Recursive Select - tree traversal

Walking a tree is not that big of a challenge. There are a few different variations in the SQL language but they are similar enough.

Given a schema that looks like:
create table tree( id int, parentid int, type int);
;with recursive    tree_cte (id, parentid, type) as (       select 1,0,0       union all       select, t.parentid, t.type         from tree t         inner join tree_cte tc on     )     select * from tree_cte tc     ;
SQL Server:
;with     tree_cte (id, parentid, type) as (       select id, parentid, type from (values(1,0,0) X(id, parentid, type, path))
       union all       select, t.parentid, t.type         from tree t         inner join tree_cte tc on     )     select * from tree_cte tc     ;
The differences are '+' instead of '||' and "recursive" and a little of the initiator SQL in the SQL Server version.

In a project I'm working on I need to create a graph of the entire tree, however, there are a few constraints. (a) the graph is huge so limit the graph as soon as possible; (b) only report full paths (no downline nodes); (c) a downline node can only be of type '1'. (NOTE: nodes of type 1 will not be separated by other node types.)

The original query returned:
Nothing special to see, it's the same as if I had selected everything:
select * from tree
Let's look at the individual paths:
;with recursive    tree_cte (id, parentid, type, path) as (       select 1,0,0,'1'       union all       select, t.parentid, t.type, tc.path || '.' || cast( as varchar)         from tree t         inner join tree_cte tc on     )     select * from tree_cte tc
With this output:
But according to my rules there are a few extra lines:
'+' when the node was the wrong type
'*' when the node was not a leaf node

This is the final code unless someone posts a recommendation... it is pretty simple:
;with recursive    tree_cte (id, parentid, type, path) as (       select 1,0,0,'1'       union all       select, t.parentid, t.type, tc.path || '.' || cast( as varchar)         from tree t         inner join tree_cte tc on         where t.type =1     )     select * from tree_cte tc     where not exists (select 1 from tree t where and type=1)
and it produced:
The differences being the where clause in the recursive SQL in the CTE and the conditional check in the outer select.
(1) where t.type =1
(2) where not exists (select 1 from tree t where and type=1)
(1) being some sort of a sentinel terminator for quick termination of the recursion instead of exhausting the data.
(2) when there is a mix of nodes where the non-desired nodes appear at different depths in the tree we need to make sure that the perceived leaf node is actually a leaf or the last of it's type.

Feels good to me. Now I have to put this into practice.


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