"How to get distinct values of sharepoint column using SSRS"

Hi,

    I have integrated sharepoint list data to SQL Server reporting services. I am using the below to query sharepoint list data using sql reporting services.

<Query>
   <SoapAction>http://schemas.microsoft.com/sharepoint/soap/GetListItems</SoapAction>
   <Method Namespace="http://schemas.microsoft.com/sharepoint/soap/" Name="GetListItems">
      <Parameters>
         <Parameter Name="listName">
            <DefaultValue>{GUID of list}</DefaultValue>
         </Parameter>
         <Parameter Name="viewName">
            <DefaultValue>{GUID of listview}</DefaultValue>
         </Parameter>
         <Parameter Name="rowLimit">
            <DefaultValue>9999</DefaultValue>
         </Parameter>           
      </Parameters>
   </Method>  
<ElementPath IgnoreNamespaces="True">*</ElementPath>
</Query>

By using this query, I am getting a dataset which includes all the columns of sharepoint list. Among these columns, I wanted to display only 2 columns (i.e Region and Sales type) using chart. I have created a Region parameter but when I click preview, the drop down box is giving me all the repeatative values of region like RG1,RG1,RG1,RG2,RG2,RG2,RG2,RG3.......... I wanted to display only distinct values of Region parameter so that whenever end user select region from the parameter drop down, it will display the respective value of Sales type column.
Also when I select only RG1 parameter, it is giving me a chart including the sales type of all the Regions. (it should display me only the sales type of RG1) How can I link these 2 columns so that they will display the values respectively.
 
          I would really appreciate if anyone can help me out with this.

Thanks,
Sam.