Passing params value by a query to multiselect param of report through Data driven subscription

I have a report (build in SSRS 2008R2)which has period_name as a multivalue parameter. I have created Data driven subscription and have written a query in subscription which fetches multiple values of period_name on a condition written. But instead of creating one report for all the param values its creating separate report for each period_name value and sending that many reports in a separate mail.

For example I have got 5 emails having report for each period_name written by that subscription query. But I want a single report for all the priod_names. Please let me know is there any setting in subscription which I need to do. This is an urgent requirement.

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Nilima