Consider the following scenario. In Microsoft SQL Server 2005, you create a table that contains a nonclustered primary key. Then, you create another table that contains a foreign key. The foreign key references the first table. Additionally, the foreign key defines one of the following cascading actions:

•	ON DELETE SET NULL
•	ON DELETE SET DEFAULT

You run a DELETE statement that uses a join in the FROM clause against the first table. In this scenario, you may receive the following error message:

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This issue occurs because the join in the FROM clause may produce multiple copies of a given target row. However, the delete operator should only delete a row one time. Therefore, the execution plan has to have an additional operator between the join and the delete operator. This additional operator will eliminate duplicate rows. The additional operator only produces required information about the target row to locate it in the heap of the table or in the clustered index. To implement the cascading action, SQL Server 2005 adds a join before the delete operator. It does this by using the primary key values of the deleted rows to find corresponding rows in the foreign table. If the primary key is the clustering key, the join can use the locator information that is produced by the additional operator. However, if the primary key is a nonclustered primary key, the information that is produced by the additional operator differs from the information that is required by the join. Therefore, SQL Server 2005 generates an incorrect execution plan.

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The fix for this issue was first released in Cumulative Update 8. For more information about how to obtain this cumulative update package for SQL Server 2005 Service Pack 2, click the following article number to view the article in the Microsoft Knowledge Base:Note Because the builds are cumulative, each new fix release contains all the hotfixes and all the security fixes that were included with the previous SQL Server 2005 fix release. Microsoft recommends that you consider applying the most recent fix release that contains this hotfix. For more information, click the following article number to view the article in the Microsoft Knowledge Base:Microsoft SQL Server 2005 hotfixes are created for specific SQL Server service packs. You must apply a SQL Server 2005 Service Pack 2 hotfix to an installation of SQL Server 2005 Service Pack 2. By default, any hotfix that is provided in a SQL Server service pack is included in the next SQL Server service pack.

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To work around this problem, use one of the following methods:

•	Create a clustered primary key instead of a nonclustered primary key in the table against which you run the DELETE statement.
•	Rewrite the DELETE statement to avoid the duplicate rows. For example, you have the following problematic query. DELETE Table1 FROM Table1 JOIN Table2 on Table1.col1 = Table2.col1 You can rewrite the query as the following. WITH cte AS ( SELECT c FROM Table1 WHERE Table1.col1 IN (SELECT col1 FROM Table2) ) DELETE cte;
•	Remove the cascading action from the foreign key.

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Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.

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For more information about what files are changed, and for information about any prerequisites to apply the cumulative update package that contains the hotfix that is described in this Microsoft Knowledge Base article, click the following article number to view the article in the Microsoft Knowledge Base:

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For more information about the list of builds that are available after SQL Server Service Pack 2, click the following article number to view the article in the Microsoft Knowledge Base: For more information about the Incremental Servicing Model for SQL Server, click the following article number to view the article in the Microsoft Knowledge Base:For more information about how to obtain SQL Server 2005 Service Pack 2, click the following article number to view the article in the Microsoft Knowledge Base: For more information about the new features and the improvements in SQL Server 2005 Service Pack 2, visit the following Microsoft Web site: For more information about the naming schema for SQL Server updates, click the following article number to view the article in the Microsoft Knowledge Base:For more information about software update terminology, click the following article number to view the article in the Microsoft Knowledge Base:

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