temp_vs_var_var_reads.sql

select 
	DB_NAME(mf.database_id)
	,sum(fs.num_of_reads) as total_reads
from sys.master_files mf
cross apply sys.dm_io_virtual_file_stats(mf.database_id,NULL) fs
where mf.database_id = 2
and mf.type_desc = 'ROWS' 
group by mf.database_id
GO
DECLARE @temp1 TABLE (col1 int)
insert into @temp1 select database_id from sys.databases
DBCC DROPCLEANBUFFERS
select count(*) from @temp1
GO
select 
	DB_NAME(mf.database_id)
	,sum(fs.num_of_reads) as total_reads
from sys.master_files mf
cross apply sys.dm_io_virtual_file_stats(mf.database_id,NULL) fs
where mf.database_id = 2
and mf.type_desc = 'ROWS' 
group by mf.database_id
GO