They cannot drag fields.
Instead you can provide Adhoc Reporting functionality.
Attached is an example.
Adhoc Report.qvw 162.0 K
Thanks for inputs and files it is very nice. now I got some idea on Drag fields. Unless we select one dim we could not see the table in your attached adhoc.qvw file
I have small changes in my requirement. I have some fixed dimension and expression in table, in addition if the user select any dimension in "pick dimension list" it should be added or removed.
Can you please help me on the new requirement.