FIX: Incorrect Results From a Parallel Query That Uses a UNION and Variables or Parameters

View products that this article applies to.

SYMPTOMS

You may receive incorrect results, if your query meets the following conditions:

The query specifies a UNION or a UNION ALL of two or more inputs.
In the UNION, at least one of the SELECT statements return the parameter or variable value (that is, it uses this value in the select list and not in the where clause).
The column returning the variable or parameter value is being used as a join or grouping column higher in the query tree, and this operator is run in parallel, requiring that the data stream be partitioned based on the join or grouping columns.

The following query is an example of one that is subject to this problem:

DECLARE @a SMALLINT
SET @a=1

SELECT yy, COUNT(*) 
FROM ( 
	SELECT productid xx, @a yy FROM products
	UNION ALL
	SELECT productid xx, unitsinstock yy FROM products
     ) zz
GROUP BY yy

Note This query is not a reproduce scenario for the Northwind database. It is only there to show the form and syntax of a hypothetical query on a hypothetical table named products.

Back to the top

To resolve this problem, obtain the latest service pack for Microsoft SQL Server 2000. For additional information, click the following article number to view the article in the Microsoft Knowledge Base:

290211 (http://support.microsoft.com/kb/290211/ ) How to obtain the latest SQL Server 2000 service pack

Back to the top

Hotfix information

The English version of this fix has the file attributes (or later) that are listed in the following table. The dates and times for these files are listed in coordinated universal time (UTC). When you view the file information, it is converted to local time. To find the difference between UTC and local time, use the Time Zone tab in the Date and Time tool in Control Panel.

   Date         Time   Version         Size             File name
   ---------------------------------------------------------------------------
   31-May-2003  18:45  2000.80.818.0      78,400 bytes  Console.exe      
   25-Jun-2003  01:01  2000.80.818.0      33,340 bytes  Dbmslpcn.dll     
   25-Apr-2003  02:12                    786,432 bytes  Distmdl.ldf
   25-Apr-2003  02:12                  2,359,296 bytes  Distmdl.mdf
   30-Jan-2003  01:55                        180 bytes  Drop_repl_hotfix.sql
   23-Jun-2003  22:40  2000.80.837.0   1,557,052 bytes  Dtsui.dll        
   23-Jun-2003  22:40  2000.80.837.0     639,552 bytes  Dtswiz.dll       
   24-Apr-2003  02:51                    747,927 bytes  Instdist.sql
   03-May-2003  01:56                      1,581 bytes  Inst_repl_hotfix.sql
   08-Feb-2003  06:40  2000.80.765.0      90,692 bytes  Msgprox.dll      
   01-Apr-2003  02:07                      1,873 bytes  Odsole.sql
   05-Apr-2003  01:46  2000.80.800.0      62,024 bytes  Odsole70.dll     
   07-May-2003  20:41  2000.80.819.0      25,144 bytes  Opends60.dll     
   02-Apr-2003  21:48  2000.80.796.0      57,904 bytes  Osql.exe         
   02-Apr-2003  23:15  2000.80.797.0     279,104 bytes  Pfutil80.dll     
   22-May-2003  22:57                     19,195 bytes  Qfe469571.sql
   12-Jun-2003  16:37                  1,083,989 bytes  Replmerg.sql
   04-Apr-2003  21:53  2000.80.798.0     221,768 bytes  Replprov.dll     
   08-Feb-2003  06:40  2000.80.765.0     307,784 bytes  Replrec.dll      
   05-May-2003  00:05                  1,085,874 bytes  Replsys.sql
   01-Jun-2003  01:01  2000.80.818.0     492,096 bytes  Semobj.dll       
   31-May-2003  18:27  2000.80.818.0     172,032 bytes  Semobj.rll
   29-May-2003  00:29                    115,944 bytes  Sp3_serv_uni.sql
   01-Jun-2003  01:01  2000.80.818.0   4,215,360 bytes  Sqldmo.dll       
   07-Apr-2003  17:44                     25,172 bytes  Sqldumper.exe    
   19-Mar-2003  18:20  2000.80.789.0      28,672 bytes  Sqlevn70.rll
   02-Jul-2003  00:18  2000.80.834.0     180,736 bytes  Sqlmap70.dll     
   08-Feb-2003  06:40  2000.80.765.0      57,920 bytes  Sqlrepss.dll     
   23-Jun-2003  22:40  2000.80.837.0   7,553,105 bytes  Sqlservr.exe     
   08-Feb-2003  06:40  2000.80.765.0      45,644 bytes  Sqlvdi.dll       
   25-Jun-2003  01:01  2000.80.818.0      33,340 bytes  Ssmslpcn.dll     
   01-Jun-2003  01:01  2000.80.818.0      82,492 bytes  Ssnetlib.dll     
   01-Jun-2003  01:01  2000.80.818.0      25,148 bytes  Ssnmpn70.dll     
   01-Jun-2003  01:01  2000.80.818.0     158,240 bytes  Svrnetcn.dll     
   31-May-2003  18:59  2000.80.818.0      76,416 bytes  Svrnetcn.exe     
   30-Apr-2003  23:52  2000.80.816.0      45,132 bytes  Ums.dll          
   02-Jul-2003  00:19  2000.80.834.0      98,816 bytes  Xpweb70.dll

Note Because of file dependencies, the most recent hotfix or feature that contains the files may also contain additional files.

Back to the top

WORKAROUND

One of the requirements to result in this incorrect results scenario is that the query picks a parallel plan. To work around this problem, you can disable parallelism either at the query level by using a "MAXDOP 1" hint (see SQL Server Books Online for more information), or at a server level by setting the configuration parameter "Max Degree of Parallelism" to 1 (by using the sp_configure stored procedure).

Back to the top

STATUS

Microsoft has confirmed that this is a problem in the Microsoft products that are listed at the beginning of this article. This problem was first corrected in Microsoft SQL Server 2000 Service Pack 4.

Back to the top