my dataset from sharepoint list. and this dataset value assign to parameter. i want when no any parameter is selected than it should filter like "ALL". when i select alow null value it give me prompt error you  can not select null in multivalue parameter.

How can i do it. i am using share point

Hi Asif,

When we create a parameter and select Allow Blank value, we should add a <Blank> () value in the list of available values if we want it to be allowed as valid.
In order to meet your requirement, please refer to the following steps:
  1. Specify the dataset query as follows:
      SELECT columns
      FROM Table 
      WHERE (column_name  in (@Parameter)  or in(@parameter)).
 2. Specify the available values for the parameter. If the values are specified values, please add a blank value. If available values retrieved form a query, please refer to the following query:
    SELECT DISTINCT column
    FROM           table
    UNION
    SELECT as column
    FROM   table
 3. Add the blank value as default value for the parameter.
The following scree shot show preview of a test report. Please take as reference.

The following thread is about the same issue, please see:
http://social.msdn.microsoft.com/Forums/en-AU/sqlreportingservices/thread/dfd4efd2-fc0f-4ba2-b225-ce5f7f1e2a96

Milan,

Thank you for your reply. but problem is that i am fetching data from share point list.. where i cant write any query.

Hi Mehmood,

In Reporting Services, if the report parameter is multivalued, its not supported to enable Allow null value option. In your scenario, since you are retrieving data from SharePoint list then use those values as parameter available values, to enable NULL value for the parameter to filter the report, we can add one record which is NULL value to the query results. Then the NULL value will display in parameter drop-down list. If the SharePoint list contains NULL value, parameter drop-down list also contains NULL for us to select then filter.

After creating a parameter, we must select values for the parameter if it doesnt contain default values. So in your scenario, since parameter is multivalued, you can select <Select All> from parameter drop-down list, or you can specify the default values for the parameter against the SharePoint list to display all records in the report when previewing the report.

If you have any question, please feel free to ask.

Best regards,
Qiuyun Yu