Microsoft KB Archive/830887

= FIX: Some queries that have a left outer join and an IS NULL filter run slower after you install SQL Server 2000 post-SP3 hotfix =

Article ID: 830887

Article Last Modified on 11/2/2007

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APPLIES TO


 * Microsoft SQL Server 2000 Developer Edition
 * Microsoft SQL Server 2000 Standard Edition
 * Microsoft SQL Server 2000 Enterprise Edition
 * Microsoft SQL Server 2000 Personal Edition
 * Microsoft SQL Server 2000 Enterprise Edition
 * Microsoft SQL Server 2000 Workgroup Edition
 * Microsoft SQL Server 2000 Desktop Engine (Windows)
 * Microsoft SQL Server 2000 Developer Edition
 * Microsoft SQL Server 2000 Enterprise Edition 64-bit

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Bug #: SHILOH_BUGS (470434)



SYMPTOMS
A query may run slower against Microsoft SQL Server 2000 post-SP3 hotfix build 8.00.0776 or later when compared to queries that run against SQL Server 2000 before hotfix build 8.00.0776, if the following conditions are true:
 * The query involves a left outer join of two tables. In the following example, table 1 is the left table and table 2 is the right table.
 * An IS NULL filter condition exists on a column for the right table (table 2).
 * The joining columns have different data types. One column is of type varchar/char, and the other column is of type nvarchar/nchar.
 * Very few of the query result rows satisfy the ON condition of the outer join.

For example, a query that contain the following join and filter condition may run slower: t1 left outer join t2 on t1.c1 = t2.c1 where t2.c1 is null --t1.c1 is of type nvarchar and t2.c1 is of type varchar



CAUSE
This problem occurs because the SQL Server optimizer underestimates the number of rows that satisfies the IS NULL filter condition after the join.



WORKAROUND
To work around this problem, make sure that the joining columns are of the same data type.



Service pack information
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 How to obtain the latest SQL Server 2000 service pack

Hotfix information
The English version of this hotfix 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 16:45  2000.80.818.0      78,400  Console.exe 28-Oct-2003 02:21  2000.80.873.0     315,968  Custtask.dll 02-Oct-2003 18:59  2000.80.867.0      33,340  Dbmslpcn.dll 25-Apr-2003 00:12                    786,432  Distmdl.ldf 25-Apr-2003 00:12                  2,359,296  Distmdl.mdf 29-Jan-2003 23:55                        180  Drop_repl_hotfix.sql 12-Sep-2003 01:26  2000.80.859.0   1,905,216  Dtspkg.dll 26-Aug-2003 18:16  2000.80.854.0     528,960  Dtspump.dll 23-Jun-2003 20:40  2000.80.837.0   1,557,052  Dtsui.dll 23-Jun-2003 20:40  2000.80.837.0     639,552  Dtswiz.dll 24-Apr-2003 00:51                    747,927  Instdist.sql 02-May-2003 23:56                      1,581  Inst_repl_hotfix.sql 08-Feb-2003 04:40  2000.80.765.0      90,692  Msgprox.dll 01-Apr-2003 00:07                      1,873  Odsole.sql 04-Apr-2003 23:46  2000.80.800.0      62,024  Odsole70.dll 07-May-2003 18:41  2000.80.819.0      25,144  Opends60.dll 02-Apr-2003 19:48  2000.80.796.0      57,904  Osql.exe 02-Apr-2003 21:15  2000.80.797.0     279,104  Pfutil80.dll 04-Aug-2003 16:17                    550,780  Procsyst.sql 11-Sep-2003 22:37                     12,305  Qfe469315.sql 22-May-2003 20:57                     19,195  Qfe469571.sql 05-Sep-2003 23:36                  1,090,932  Replmerg.sql 06-Sep-2003 05:18  2000.80.858.0     221,768  Replprov.dll 06-Sep-2003 05:18  2000.80.858.0     307,784  Replrec.dll 05-Sep-2003 22:00                  1,087,150  Replsys.sql 13-Aug-2003 14:28                    986,603  Repltran.sql 21-Oct-2003 22:08  2000.80.871.0      57,916  Semnt.dll 29-Jul-2003 18:13  2000.80.819.0     492,096  Semobj.dll 31-May-2003 16:27  2000.80.818.0     172,032  Semobj.rll 05-Aug-2003 19:06                    127,884  Sp3_serv_uni.sql 31-May-2003 23:01  2000.80.818.0   4,215,360  Sqldmo.dll 07-Apr-2003 15:44                     25,172  Sqldumper.exe 19-Mar-2003 16:20  2000.80.789.0      28,672  Sqlevn70.rll 27-Sep-2003 02:42  2000.80.865.0     180,792  Sqlmap70.dll 03-Sep-2003 00:56  2000.80.857.0     188,992  Sqlmmc.dll 02-Sep-2003 21:03  2000.80.857.0     479,232  Sqlmmc.rll 21-Oct-2003 22:08  2000.80.871.0     401,984  Sqlqry.dll 08-Feb-2003 04:40  2000.80.765.0      57,920  Sqlrepss.dll 28-Oct-2003 02:21  2000.80.873.0   7,606,353  Sqlservr.exe 25-Jul-2003 19:44  2000.80.845.0     590,396  Sqlsort.dll 08-Feb-2003 04:40  2000.80.765.0      45,644  Sqlvdi.dll 02-Oct-2003 18:59  2000.80.867.0      33,340  Ssmslpcn.dll 31-May-2003 23:01  2000.80.818.0      82,492  Ssnetlib.dll 31-May-2003 23:01  2000.80.818.0      25,148  Ssnmpn70.dll 28-Oct-2003 02:21  2000.80.873.0     123,456  Stardds.dll 31-May-2003 23:01  2000.80.818.0     158,240  Svrnetcn.dll 31-May-2003 16:59  2000.80.818.0      76,416  Svrnetcn.exe 30-Apr-2003 21:52  2000.80.816.0      45,132  Ums.dll 01-Jul-2003 22:19  2000.80.834.0      98,816  Xpweb70.dll Note Because of file dependencies, the most recent hotfix or feature that contains these files may also contain additional files.



STATUS
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the &quot;Applies to&quot; section of this article.

This problem was first corrected in Microsoft SQL Server 2000 Service Pack 4.



MORE INFORMATION
After you install the hotfix that is described in this article, you must make sure that trace flag 9209 is turned on when you start SQL Server. For this fix to take effect, you must have trace flag 9209 turned on when you start SQL Server. To do so, follow these steps:
 * 1) Start SQL Server Enterprise Manager.
 * 2) Right-click the instance of SQL Server, and then click Properties.
 * 3) Click the General tab, and then click Startup Parameters.
 * 4) In the Startup Parameters dialog box, type -T9209 in Parameter box, click Add, and then click OK.
 * 5) In the SQL Server Properties dialog box, click OK.
 * 6) Restart SQL Server.

Data type conversions (in this case, when an nvarchar/nchar column is compared to a varchar/char column) on a column in a query may have an adverse effect on the query's performance, and it is a good idea to avoid doing so if you can. If you use data type conversions, SQL Server may not be able to accurately produce cardinality estimates. SQL Server may also be restricted from using appropriate indexes. For additional information about data type conversions, click the following article number to view the article in the Microsoft Knowledge Base:

271566 PRB: SQL Server comparisons between columns and constants with different data types

Keywords: kbbug kbfix kbqfe kbsqlserv2000presp4fix kbhotfixserver KB830887

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