Do you mean that you do not have the distinct count option for your calculated field? If this is the case, not all data bases support this function (i.e. JET). One way around this is to create an extract.
Hope this helps!
Thanks for reply. My DB is MS Access, It is having distinct count function.Whether Tableau is having distinct count function? or any other method to achieve the result.Or i have to create a standalone query to achieve objective.