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

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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.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.This problem was first corrected in Microsoft SQL Server 2000 Service Pack 4.
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 "Symptoms" 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.

Article ID: 823514 - Last Review: 02/27/2014 18:44:24 - Revision: 13.2

  • 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)
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