Microsoft KB Archive/823514

= FIX: Build 8.00.0837: A query that contains a correlated subquery runs slowly =

Article ID: 823514

Article Last Modified on 10/25/2005

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APPLIES TO


 * Microsoft SQL Server 2000 Enterprise Edition
 * Microsoft SQL Server 2000 Developer Edition
 * Microsoft SQL Server 2000 Standard Edition
 * Microsoft SQL Server 2000 Desktop Engine (Windows)
 * Microsoft SQL Server 2000 Enterprise Edition

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SYMPTOMS
If you have a set of predicates in the following form

(a = b) && (a = constant)

there is an implied redundant predicate (b = constant) that can be added. The absence of this implied predicate can make the query run slowly.

An enhancement has been made to SQL Server to add this redundant predicate for semi joins, anti-semi joins, inner joins, and outer joins.



Service pack information
To resolve this problem, obtain the latest service pack for Microsoft SQL Server 2000. For more 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 file attributes) 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   Console.exe 25-Jun-2003 01:01  2000.80.818.0       33,340   Dbmslpcn.dll 25-Apr-2003 02:12                     786,432   Distmdl.ldf 25-Apr-2003 02:12                   2,359,296   Distmdl.mdf 30-Jan-2003 01:55                         180   Drop_repl_hotfix.sql 23-Jun-2003 22:40  2000.80.837.0    1,557,052   Dtsui.dll 23-Jun-2003 22:40  2000.80.837.0      639,552   Dtswiz.dll 24-Apr-2003 02:51                     747,927   Instdist.sql 03-May-2003 01:56                       1,581   Inst_repl_hotfix.sql 08-Feb-2003 06:40  2000.80.765.0       90,692   Msgprox.dll 01-Apr-2003 02:07                       1,873   Odsole.sql 05-Apr-2003 01:46  2000.80.800.0       62,024   Odsole70.dll 07-May-2003 20:41  2000.80.819.0       25,144   Opends60.dll 02-Apr-2003 21:48  2000.80.796.0       57,904   Osql.exe 02-Apr-2003 23:15  2000.80.797.0      279,104   Pfutil80.dll 22-May-2003 22:57                      19,195   Qfe469571.sql 12-Jun-2003 16:37                   1,083,989   Replmerg.sql 04-Apr-2003 21:53  2000.80.798.0      221,768   Replprov.dll 08-Feb-2003 06:40  2000.80.765.0      307,784   Replrec.dll 05-May-2003 00:05                   1,085,874   Replsys.sql 01-Jun-2003 01:01  2000.80.818.0      492,096   Semobj.dll 31-May-2003 18:27  2000.80.818.0      172,032   Semobj.rll 29-May-2003 00:29                     115,944   Sp3_serv_uni.sql 01-Jun-2003 01:01  2000.80.818.0    4,215,360   Sqldmo.dll 07-Apr-2003 17:44                      25,172   Sqldumper.exe 19-Mar-2003 18:20  2000.80.789.0       28,672   Sqlevn70.rll 02-Jul-2003 00:18  2000.80.834.0      180,736   Sqlmap70.dll 08-Feb-2003 06:40  2000.80.765.0       57,920   Sqlrepss.dll 23-Jun-2003 22:40  2000.80.837.0    7,553,105   Sqlservr.exe 08-Feb-2003 06:40  2000.80.765.0       45,644   Sqlvdi.dll 25-Jun-2003 01:01  2000.80.818.0       33,340   Ssmslpcn.dll 01-Jun-2003 01:01  2000.80.818.0       82,492   Ssnetlib.dll 01-Jun-2003 01:01  2000.80.818.0       25,148   Ssnmpn70.dll 01-Jun-2003 01:01  2000.80.818.0      158,240   Svrnetcn.dll 31-May-2003 18:59  2000.80.818.0       76,416   Svrnetcn.exe 30-Apr-2003 23:52  2000.80.816.0       45,132   Ums.dll 02-Jul-2003 00:19  2000.80.834.0       98,816   Xpweb70.dll Note Because of file dependencies, the most recent hotfix or feature that contains the 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.This problem was first corrected in Microsoft SQL Server 2000 Service Pack 4.



MORE INFORMATION
When you apply a hotfix or service pack that contains this fix, the SQL Server optimizer automatically introduces the implied predicate and may remove the corresponding join predicate.

The example that is mentioned in the &quot;Symptoms&quot; section shows a join between a and b. In this example, after optimization the predicate looks like the following:

(a = constant) and (b = constant)

When the original predicate is from a multicolumn key, the simplified expression may remove one of the original join keys. For example, the predicate t1.a = t2.a && t1.b = t2.b && t1.c = constant is changed to t1.b = t2.b && t1.a = constant && t2.a = constant. If column a is the leading column of a multicolumn index, you cannot use a multicolumn density match for cardinality estimation. Additionally, this may cause query plans where the query plan seeks on only the leading index column and applies the remaining filter criteria as residual filters in a WHERE clause on the index seek line or in a WHERE clause for the join operator. For example, the query plan seeks on t1.a = constant. In this scenario, there may be greater disk input/output load and increased CPU utilization. In SQL Server 2000 SP4, you can disable this optimization through trace flag 9061.

Keywords: kbbug kbfix kbsqlserv2000presp4fea kbqfe kbsqlserv2000presp4fix kbhotfixserver KB823514

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