SQL-Abfrage mit unterschiedlichen Ergebnissen

SELECT   DISTINCT([volume_mount_point]), [available_bytes] 
FROM     [sys].[master_files] AS [f] CROSS APPLY 
         [sys].[dm_os_volume_stats]([f].[database_id], [f].[file_id]) 
GROUP BY [volume_mount_point], [available_bytes] 
ORDER BY 1

volume_mount_point                    available_bytes
L:\                                   434136416256
L:\MSSQL11.xxxxx\MSSQL\DATA\yyyy\     86200115200

Dim µReturnValue As SqlDataReader = Nothing

Dim µConnectionString = String.Format(
      "Server={0};DataBase={1};uid={2};pwd={3}",  
      mDbServerInstance, mDatabaseName, mUserName, mPassword
    )

Dim µQueryString = "SELECT   DISTINCT([volume_mount_point]), [available_bytes] " &  
                   "FROM     [sys].[master_files] AS [f] CROSS APPLY " &  
                   "         [sys].[dm_os_volume_stats]([f].[database_id], [f].[file_id]) " &  
                   "GROUP BY [volume_mount_point], [available_bytes] " &  
                   "ORDER BY 1"  

Dim µCon As New SqlConnection(µConnectionString)
µCon.Open()
Using µCmd As New SqlCommand(µQueryString, µCon)
  µReturnValue = µCmd.ExecuteReader(CommandBehavior.CloseConnection)
End Using