Common Table Expression to traverse down hierarchy - sql

Question

The Structure
I have 2 tables that link to each other. One is a set of values and a nullable foreign key that points to the Id of the other table, which contains 2 foreign keys back to the other table.
HierarchicalTable
Id LeftId RightId SomeValue
1 1 2 some value
2 3 4 top level in tree
3 5 6 incorrect hierarchy 1
4 7 8 incorrect result top level
IntermediateTable
Id SomeValue HierarchicalTableId
1 some value NULL
2 value NULL
3 NULL 1
4 value NULL
5 incorrect result 1 NULL
6 incorrect result 3 NULL
7 incorrect result 3 NULL
8 NULL 3
Each table points down the hierarchy. Here is this structure graphed out for the Hierarchical Table records 1 & 2 and their IntermediateTable values:
(H : HierarchicalTable, I : IntermediateTable)
H-2
/ \
I-3 I-4
/
H-1
/ \
I-1 I-2
The Problem
I need to be able to send in an Id for a given HierarchicalTable and get all the HierarchicalTable records below it. So, for the structure above, if I pass 1 into a query, I should just get H-1 (and from that, I can load the related IntermediateTable values). If I pass 2, I should get H-2 and H-1 (and, again, use those to load the relevant IntermediateTable values).
The Attempts
I've tried using a CTE, but there are a few main things that are different from the examples I've seen:
In my structure, the objects point down to their children, instead of up to their parent
I have the Id of the top object, not the Id of the bottom object.
My hierarchy is split across 2 tables. This shouldn't be a big issue once I understand the algorithm to find the results I need, but this could be causing additional confusion for me.
If I run this query:
declare #TargetId bigint = 2
;
with test as (
select h.*
from dbo.hierarchicaltable h
inner join dbo.intermediatetable i
on (h.leftid = i.id or h.rightid = i.id)
union all
select h.*
from dbo.hierarchicaltable h
where h.id = #TargetId
)
select distinct *
from test
I get all 4 records in the HierarchicalTable, instead of just records 1 & 2. I'm not sure if what I want is possible to do with a CTE.

Answer 1

Try this:
I'm build entire tree with both tables, then filter (only hierarchicaltable records).
DECLARE #HierarchicalTable TABLE(
Id INT,
LeftId INT,
RightId INT,
SomeValue VARCHAR(MAX)
)
INSERT INTO #HierarchicalTable
VALUES
(1, 1, 2, 'some value '),
(2, 3, 4, 'top level in tree '),
(3, 5, 6, 'incorrect hierarchy 1 '),
(4, 7, 8, 'incorrect result top level')
DECLARE #IntermediateTable TABLE(
Id INT,
SomeValue VARCHAR(MAX),
HierarchicalTableId INT
)
INSERT INTO #IntermediateTable
VALUES
(1, 'some value' ,NULL ),
(2, 'value ' ,NULL ),
(3, NULL ,1 ),
(4, 'value ' ,NULL ),
(5, 'incorrect result 1' ,NULL ),
(6, 'incorrect result 3' ,NULL ),
(7, 'incorrect result 3' ,NULL ),
(8, NULL ,3 )
DECLARE #TargetId INT = 2;
WITH CTE AS (
SELECT Id AS ResultId, LeftId, RightId, NULL AS HierarchicalTableId
FROM #HierarchicalTable
WHERE Id = #TargetId
UNION ALL
SELECT C.Id AS ResultId, C.LeftId, C.RightId, NULL AS HierarchicalTableId
FROM #HierarchicalTable C
INNER JOIN CTE P ON P.HierarchicalTableId = C.Id
UNION ALL
SELECT NULL AS ResultId, NULL AS LeftId, NULL AS RightId, C.HierarchicalTableId
FROM #IntermediateTable C
INNER JOIN CTE P ON P.LeftId = C.Id OR P.RightId = C.Id
)
SELECT *
FROM CTE
WHERE ResultId IS NOT NULL