Assume that you use Microsoft SQL Server 2014. When you query about Dynamic Management Views (DMV) sys.dm_exec_requests in Microsoft SQL Server Management Studio (SSMS) by using Select * From sys.dm_exec_requests, you find that the values of column query_hash and query_plan_hash are NULL.
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Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.