Unexpected result from CTE on cyclic data - sql-server

Question

I have this table:
CREATE TABLE [dbo].[hierarchical] (
[id] INT NOT NULL,
[parent_id] INT NULL,
[name] NVARCHAR (40) NULL
);
Containing some data:
INSERT INTO [dbo].[hierarchical] ([id], [parent_id], [name]) VALUES (9, 11, N'43EB7203-3A7F-49A9-8C58-F18738D2BBC4')
INSERT INTO [dbo].[hierarchical] ([id], [parent_id], [name]) VALUES (10, 9, N'E202CAFA-4C0D-4A84-B02A-BF53AC3AFAB1')
INSERT INTO [dbo].[hierarchical] ([id], [parent_id], [name]) VALUES (11, 10, N'371C28E0-8C54-4A23-B28A-273979810E54')
As you can see the hierarchy is cyclical 9 => 11 => 10 => 9.
I'm trying to create a CTE that can handle this cyclic data like this:
alter procedure GetHierarchicalTree
#rootid int
as begin
;with computed as (
select H.id, H.parent_id, 1 lvl, '[' + cast(H.id as nvarchar(max)) + ']' pat
from hierarchical H
where id = #rootid
union all
select H.id, H.parent_id, C.lvl + 1, C.pat + '[' + CAST(H.id as nvarchar(max)) + ']'
from computed C
inner join hierarchical H on C.id = H.parent_id
where C.pat not like '%[' + cast(H.id as nvarchar(max)) + ']%'
)
select * from computed
option (maxrecursion 0)
end
The guard clause is the where C.pat not like '%[' + cast(H.id as nvarchar(max)) + ']%' so if the ID is already included then stop.
But when running the stored procedure on ID number 9:
exec gethierarchicaltree 9
The sp returns 9 and 10, but not 11, which is odd because 11 shouldn't be in computed.pat already.
Running on 11 returns 9 and 11, but not 10.
Even more puzzling is running on 10, because the sp only returns 10.
Why the sp doesn't return 9 and 11?

Answer 1

I think your problem is in the LIKE, the square brackets [] should not be there:
where C.pat not like '%' + cast(H.id as nvarchar(max)) + '%'
UPDATE:
I understand you use the brackets to delimit your path. In that case you have to escape the opening bracket like this:
where C.pat not like '%[[]' + cast(H.id as nvarchar(max)) + ']%'

Answer 2

You can also change the where condition to use charindex:
CHARINDEX('[' + cast(H.id as nvarchar(max)) + ']',C.pat)=0

Answer 3

Your data has circular reference; 11 is the parent of 9, which is the parent of 10, which is the parent of 11, which is the parent of 9, which... That isn't a hierarchy and actually infers there's a design flaw somewhere.
I suspect what you want is:
CREATE PROCEDURE dbo.GetHierarchicalTree #rootid int
AS BEGIN
WITH rCTE AS
(SELECT H.id,
H.parent_id,
CONVERT(varchar(MAX), QUOTENAME(H.id)) AS [name]
FROM dbo.hierarchical H
WHERE H.id = #rootid
UNION ALL
SELECT H.id,
H.parent_id,
r.[name] + CONVERT(varchar(MAX), QUOTENAME(H.id))
FROM rCTE r
JOIN dbo.hierarchical H ON r.parent_id = H.id
AND h.ID != #rootid)
SELECT *
FROM rCTE
--OPTION (MAXRECURSION 0); --As you have a circular reference I strongly recommend this OPTION. You could very overwhelm your server.
END;
GO
EXEC dbo.GetHierarchicalTree 9;