?
Solved

Recursive SQL Infinite loop

Posted on 2011-09-20
7
Medium Priority
?
1,851 Views
Last Modified: 2012-05-12
Hi,

I Have a table like below

ProductID          RepProdID
######            ###########
a1                       b1
b1                       c1
c1                        d1

Means, The product a1 is replaced by b1 and b1 by c1 etc

Now, If I query with product ID "a1" then I want the output

b1
c1
d1

Since product "a1" is the source of all this products.

If I query with product ID "b1" then I want the output

c1
d1

I was using the below query to achieve this.

DECLARE @ProductID VARCHAR(5)
SET @ProductID = 'a1'

;WITH CTE
AS
(
      SELECT RepProdID, 0 AS [Level]
      FROM   YourTable
      WHERE ProductID = @ProductID
      UNION ALL
      SELECT  a.RepProdID, [Level] + 1
      FROM   YourTable a INNER JOIN CTE b ON b.RepProdID = a.ProductID
)
SELECT  RepProdID FROM   CTE

All are fine, but if I have a below data in the table, then the recursion enters into infinite loop and the query fails. How can I alter the above query

ProductID          RepProdID
######            ###########
a1                       b1
b1                       a1
0
Comment
Question by:radcaesar
[X]
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
7 Comments
 
LVL 50

Accepted Solution

by:
Lowfatspread earned 2000 total points
ID: 36565814
well you shouldn't allow the table to be updated like that in the first place...
what is it supposed to represent?  (wich is the parent?)


;WITH CTE
AS
(
      SELECT RepProdID, 0 AS [Level]
      FROM   YourTable
      WHERE ProductID = @ProductID
      UNION ALL
      SELECT  a.RepProdID, [Level] + 1
      FROM   YourTable a
      INNER JOIN CTE b
      ON b.RepProdID = a.ProductID
     where not exists (select repprodid from vte as x where a.repprodid=x.repprodid
                                 and x,level < b.level + 1)
)
SELECT  RepProdID FROM   CTE

0
 
LVL 9

Author Comment

by:radcaesar
ID: 36565920
I am getting the below error when I use this,

Recursive member of a common table expression 'CTE' has multiple recursive references.

In the vte is a typo and its CTE right?
0
 
LVL 50

Expert Comment

by:Lowfatspread
ID: 36566018
yes vte was supposed to be cte

so it errors?
0
Prepare for your VMware VCP6-DCV exam.

Josh Coen and Jason Langer have prepared the latest edition of VCP study guide. Both authors have been working in the IT field for more than a decade, and both hold VMware certifications. This 163-page guide covers all 10 of the exam blueprint sections.

 
LVL 18

Expert Comment

by:deighton
ID: 36566034
the CTE is limited in how it can sub query itself - it strikes me that you could easily have a circular or infinite reference, as in fact you have there

I think instead of a recursive CTE, use a temporary table and a while loop,





0
 
LVL 9

Author Comment

by:radcaesar
ID: 36566111
No I had changed it to CTE and then this error occurs
0
 
LVL 50

Expert Comment

by:Lowfatspread
ID: 36566654
you could try this

it should stop your simple case , it wont stop a recursion chain ..  a - b , b - c , c - a   rhough

you'd need to use the temp table build loop approach...

ideally you should prevent the situation from happening by implementing a trigger to validate...
;WITH CTE
AS
(
      SELECT RepProdID, 0 AS [Level]
            ,0 as OK
      FROM   YourTable
      WHERE ProductID = @ProductID
      UNION ALL
      SELECT  a.RepProdID, [Level] + 1
        ,coalesce((select 1 from yourtable as x where x.repprodid=A.REPPORTID AND X.PRODUCTID=B.REPPRODID),0)
      FROM   YourTable a 
      INNER JOIN CTE b 
      ON b.RepProdID = a.ProductID
      AND B.OK=0
     
)
SELECT  RepProdID 
  FROM   CTE
 ORDER BY [LEVEL],REPPRODID

Open in new window

0
 
LVL 2

Expert Comment

by:grvmohan
ID: 36572194
A very simple solution:

Modify your CTE as:

;WITH CTE
AS
(
      SELECT RepProdID, 0 AS [Level]
      FROM   YourTable
      WHERE ProductID = @ProductID
      UNION ALL
      SELECT  a.RepProdID, [Level] + 1
      FROM   YourTable a INNER JOIN CTE b ON b.RepProdID = a.ProductID
      AND a.ProductID <> @ProductID
)
SELECT  RepProdID FROM   CTE
0

Featured Post

Free Backup Tool for VMware and Hyper-V

Restore full virtual machine or individual guest files from 19 common file systems directly from the backup file. Schedule VM backups with PowerShell scripts. Set desired time, lean back and let the script to notify you via email upon completion.  

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

For both online and offline retail, the cross-channel business is the most recent pattern in the B2C trade space.
Ever wondered why sometimes your SQL Server is slow or unresponsive with connections spiking up but by the time you go in, all is well? The following article will show you how to install and configure a SQL job that will send you email alerts includ…
Via a live example, show how to extract information from SQL Server on Database, Connection and Server properties
Via a live example, show how to extract insert data into a SQL Server database table using the Import/Export option and Bulk Insert.
Suggested Courses

771 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question