FIX: AV on DECLARE CURSOR with Correlated Subquery and KEYSET or DYNAMIC Cursor Type

View products that this article applies to.

This article was previously published under Q308881

BUG #: 55675 (sqlbug_70)

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SYMPTOMS

SQL Server may encounter an access violation (AV) with a DECLARE CURSOR statement if the following conditions are true:

A SELECT statement has a correlated subquery.
The correlation is through an OR clause or IN clause.
The cursor type must be KEYSET or DYNAMIC.
There is a nonclustered primary key on both correlated tables.
The subquery table must not have an additional clustered index.

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To resolve this problem, obtain the latest service pack for Microsoft SQL Server 7.0. For additional information, click the following article number to view the article in the Microsoft Knowledge Base:

301511 (http://support.microsoft.com/kb/301511/EN-US/ ) INF: How to Obtain the Latest SQL Server 7.0 Service Pack

NOTE: The following hotfix was created prior to Microsoft SQL Server 7.0 Service Pack 4.

The English version of this fix should have the following file attributes or later:

   Date         Time    Version      Size     File name
   -------------------------------------------------------

   27-SEP-2001  2:08    7.00.1010    4937KB   Sqlservr.exe

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

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WORKAROUND

You can work around this problem in the following ways:

Replace PRIMARY KEY NONCLUSTERED with PRIMARY KEY CLUSTERED.
Add a clustered index to the correlated subquery table.
Change cursor type to STATIC, FAST_FORWARD, or INSENSITIVE.
Rewrite the SELECT to avoid the correlated subquery.

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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 7.0 Service Pack 4.

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MORE INFORMATION

The following script illustrates the behavior:

---Create the tables
CREATE TABLE [dbo].[t1] (
 [id] [int] NOT NULL PRIMARY KEY NONCLUSTERED,
 [c1] [int] NOT NULL ,
 [c2] [int] NOT NULL ,
 [c3] [int] NOT NULL 
) 
GO
CREATE TABLE [dbo].[t2] ([id] [int] NOT NULL PRIMARY KEY NONCLUSTERED)
GO

---Execute the following to cause the AV
declare t cursor for
	 select (select sum(c3) from t1 where t2.id in (c1,c2)) 
          from t2
go

The short stack dump generated in the errorlog will contain the following functions:

(CSubRuleCrsFtchToUnionAllStrategy::BuildSubstitutes+f6)
(COptContext::PexprTransformTopLevel+199)
(COptContext::PexprNormalize+22)
(COptContext::PexprNormalize+a0)
(COptContext::PexprNormalize+a0)
(COptContext::PexprNormalize+a0)
(CMemo::NormalizeQuery+174)
(COptContext::PexprSearchPlan+bb)
(COptContext::PcxteOptimizeQuery+7eb)
(CQuery::Optimize+21f)
(CQuery::Prepare+92)
(CCvtTree::PqryFromTree+814)
(BuildQueryFromTree+61)
(CFetchKeyset::CompileQuery+60)
(CFetchKeyset::CompileSetFetchExp+321)
(CFetchKeyset::CompileKeysetExprs+18)
(CFetchKeyset::Compile+10f)
(CFetchComponent::smInitializeFetchComponent+fc)
(CCursorDeclareStmt::Init+286)
(CompileCursor+1f8)
(CCompPlan::FCompileStep+e79)
(CProchdr::FCompile+5d9)
(CSQLSource::FTransform+234)
(CSQLStrings::FTransform+159)
(CSQLSource::Execute+11d)
(language_exec+39c)
(execute_event+659)
(process_commands+f3)
(ProcessWorkRequests+ed)
(ThreadStartRoutine+139)
(beginthread+ce)
(CreateFileA+11b)

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