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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. Cumulative Update 12 for SQL Server 2005 Service Pack 2 contains hotfixes for SQL Server 2005 Service Pack 2 issues that have been fixed since the release of SQL Server 2005 Service Pack 2. Note This build of the cumulative update package is also known as build 9.00.3315.
Read the complete post at http://wmug.co.uk/blogs/cliffs_blog/archive/2009/02/17/sql-kb-962970-cumulative-update-package-12-for-sql-server-2005-service-pack-2.aspx