How To Set Up A Working Report Mult-Value + (Select All) Filter Dropdown in SSRS 2005

1. Set up your parameter at the report level as usual, check the box Multi-value, and set the Data Type to String

2. Set the Stored Procedure Parameter to varchar(max)  --<---- This part here is the key to it's success

Example:    @cst_key varchar(max)

3. Set  the WHERE clause to use a split string function so it can parse out the comma seperated values into an array & back out to the calling procedure.

If you already have one that splits strings into a comma seperated value, that will work fine but if you do not,
you can find a handy one here by Expert; chrismc @ http://www.experts-exchange.com/Microsoft/Development/MS-SQL-Server/SQL-Server-2005/Q_23470331.html

Then plug it into the WHERE Clause of your Stored Procedure

Example:

WHERE  
       ([cst_key] IN (SELECT VALUE FROM [dbo].[ufn_Split](@cst_key))