Recursive Query on a self referential table (not hierarchical) - sql

Question

I am creating a state chart of sorts with the data being stored in a simple self referencing table (JobPath)
JobId - ParentJobId
I was using a standard SQL CTE to get the data out which was working perfectly until I ended up with the following data
JobId - ParentId
1 2
2 3
3 4
4 2
Now as you can see Job 4 links to Job 2 which goes to Job 3 and then to Job 4 and so on.
Is there any way I can tell my query not to pull out data it already has?
Here is my current query
WITH JobPathTemp (JobId, ParentId, Level)
AS
(
-- Anchor member definition
SELECT j.JobId, jp.ParentJobId, 1 AS Level
FROM Job AS j
LEFT OUTER JOIN dbo.JobPath AS jp
ON j.JobId = jp.JobId
where j.JobId=1516
UNION ALL
-- Recursive member definition
SELECT j.JobId, jp.ParentJobId, Level + 1
FROM dbo.Job as j
INNER JOIN dbo.JobPath AS jp
ON j.JobId = jp.JobId
INNER JOIN JobPathTemp AS jpt
ON jpt.ParentId = jp.JobId
WHERE jp.ParentJobId <> jpt.JobId
)
-- Statement that executes the CTE
SELECT * FROM JobPathTemp

Answer 1

If you are not dealing with a large number of entries, the following solution might be suitable. The idea is to build the complete "id path" for each row and make sure the "current id" (in the recursive part) is not already in the path being processed:
(I removed the join to jobpath for testing purposes but the basic pattern should be the same)
WITH JobPathTemp (JobId, ParentId, Level, id_path)
AS
(
SELECT jobid,
parentid,
1 as level,
'|' + cast(jobid as varchar(max)) as id_path
FROM job
WHERE jobid = 1
UNION ALL
SELECT j.JobId,
j.parentid,
Level + 1,
jpt.id_path + '|' + cast(j.jobid as varchar(max))
FROM Job as j
INNER JOIN JobPathTemp AS jpt ON j.jobid = jpt.parentid
AND charindex('|' + cast(j.jobid as varchar), jpt.id_path) = 0
)
SELECT *
FROM JobPathTemp
;

Answer 2

This solution doesn't work, SQL Server doesn't support using UNION to join together the recursive term. Since you can't refer to the the recursion except as the join, tbh I don't see any alternative to using a stored function...
You didn't post your query... but I tried (in postgres, which works in much the same way) and if you use "UNION" (not "UNION ALL") in the recursive term, then it should automatically remove duplicate rows:
with /*recursive*/ jobs as
(select jobpath.jobid, jobpath.parentjobid from jobpath where jobid = 1
union
select jobpath.jobid, jobpath.parentjobid
from jobpath
join jobs on jobs.parentjobid = jobpath.jobid
)
select jobpath.* from jobpath join jobs on jobpath.jobid = jobs.jobid;