How to detect cyclical reference in SQL Server Query - SQL Server 2017 - sql

Question

I have a recursive WITH query in SQL Server 2017:
;WITH rec AS (
SELECT
col1 AS root_order
,col1
,col2
,col3
,col4
,col5
,col6
,col7
,col8
,col9
FROM
TableA
UNION ALL
SELECT
rec.root_order,
TableA.col2,
TableA.col3,
TableA.col4,
TableA.col5,
TableA.col6,
TableA.col7,
TableA.col8,
TableA.col9,
rec.the_level
FROM
rec
INNER JOIN TableA on rec.Details = TableA.Orders
)
SELECT DISTINCT * FROM rec
This yields a: The statement terminated. The maximum recursion 100 has been exhausted before statement completion. error.
I have tried:
OPTION (maxrecursion 0) to let it continue. But when I do that, the query infinitely loops, so that doesn't work.
In Oracle, I can use CONNECT BY ROOT and CONNECT BY PRIOR and NOCYCLE, but I know things like that aren't available in SQL Server. So I found this MSDN link which suggest something of the form:
with hierarchy
as
(
select
child,
parent,
0 as cycle,
CAST('.' as varchar(max)) + LTRIM(child) + '.' as [path]
from
#hier
where
parent is null
union all
select
c.child,
c.parent,
case when p.[path] like '%.' + LTRIM(c.child) + '.%' then 1 else 0 end as cycle,
p.[path] + LTRIM(c.child) + '.' as [path]
from
hierarchy as p
inner join
#hier as c
on p.child = c.parent
and p.cycle = 0
)
select
child,
parent,
[path]
from
hierarchy
where
cycle = 1;
go
For finding the cycles (or avoiding them). I cannot seem to take my current query and edit it in that fashion. How can I edit my current SQL to perform the cyclic reference detection like in the MSDN article?
Some sample data as requested here in SQL FIDDLE.

Answer 1

What I normally do is pretty simple. In the anchor query (the first part of the CTE), I include a value "1 AS Level" in the select list. Then in the bottom query, I select Level + 1 as the Level, so I know what depth I'm up to. Then I can just put a sanity clause into the bottom query to limit the depth i.e. WHERE LEVEL <= 10 or whatever depth you want. But yes, you still need MAXRECURSION set to 0 if you want to go above 100 levels.
Here's an example based on AdventureWorks:
WITH Materials (BillOfMaterialsID, ProductName, ProductAssemblyID, ComponentID, [Level])
AS
(
SELECT bom.BillOfMaterialsID,
p.[Name],
bom.ProductAssemblyID,
bom.ComponentID,
1
FROM Production.BillOfMaterials AS bom
INNER JOIN Production.Product AS p
ON bom.ComponentID = p.ProductID
AND bom.EndDate IS NULL
WHERE bom.ProductAssemblyID IS NULL
UNION ALL
SELECT bom.BillOfMaterialsID,
p.[Name],
bom.ProductAssemblyID,
bom.ComponentID,
m.[Level] + 1
FROM Production.BillOfMaterials AS bom
INNER JOIN Production.Product AS p
ON bom.ComponentID = p.ProductID
INNER JOIN Materials AS m
ON bom.ProductAssemblyID = BOM.ComponentID
WHERE m.[Level] <= 5
)
SELECT m.BillOfMaterialsID,
m.ProductName,
m.ProductAssemblyID,
m.ComponentID,
m.[Level]
FROM Materials AS m
ORDER BY m.[Level], m.BillOfMaterialsID;