DMF sys.dm_exec_sql_text not showing DBID

I have got this query from

http://technet.microsoft.com/en-us/library/ms181929.aspx

SELECT s2.dbid, 
    s1.sql_handle,  
    (SELECT TOP 1 SUBSTRING(s2.text,statement_start_offset / 2+1 , 
      ( (CASE WHEN statement_end_offset = -1 
         THEN (LEN(CONVERT(nvarchar(max),s2.text)) * 2) 
         ELSE statement_end_offset END)  - statement_start_offset) / 2+1))  AS sql_statement,
    execution_count, 
    plan_generation_num, 
    last_execution_time,   
    total_worker_time, 
    last_worker_time, 
    min_worker_time, 
    max_worker_time,
    total_physical_reads, 
    last_physical_reads, 
    min_physical_reads,  
    max_physical_reads,  
    total_logical_writes, 
    last_logical_writes, 
    min_logical_writes, 
    max_logical_writes  
FROM sys.dm_exec_query_stats AS s1 
CROSS APPLY sys.dm_exec_sql_text(sql_handle) AS s2  
WHERE s2.objectid is null 
ORDER BY s1.sql_handle, s1.statement_start_offset, s1.statement_end_offset;

When i execute it the dbid field is returned as null. Why this behave like this? I want to limit queries from one database but it seems not working.

Many thanks prior to your answers.

1) This behavior is available in SQL2005 -> SQL2008R2.

2) Why sys.dm_exec_sql_text.dbid has (sometimes) NULLs ?

• Within SQL2005 -> SQL2008R2 dbid is NULL "for ad hoc and prepared SQL statements" (see MSDN for SQL Server 2008 R2).
• Within SQL 2012 "For ad hoc and prepared SQL statements, the ID of the database where the statements were compiled" (see MSDN). So, starting from SQL2012 dbid will return a non-NULL value including "ad hoc and prepared SQL statements".

3) To solve this problem in SQL2008 -> SQL2008R2 I used sys.dm_exec_plan_attributes (see MSDN)

SELECT ..., ISNULL(s2.dbid,CONVERT(SMALLINT,att.value)) AS my_dbid, ...
FROM sys.dm_exec_query_stats AS s1 
CROSS APPLY sys.dm_exec_sql_text(sql_handle) AS s2 
CROSS APPLY sys.dm_exec_plan_attributes(s1.plan_handle) att
WHERE att.attribute='dbid