Handling Optional Query Parameters

I have a GridView bound to an DataSource query with parameters tied to form controls.

What is the standard / best-practices way to handle optional query parameters?

From stackoverflow

• Something like.. set the control parameter to -1 then in your query do something like...

  Select * From Blah Where
  (Somefield = @param or @param = -1)
  

• On your DataSource, have your ControlParam use the DefaultValue:

  <asp:ControlParameter Name="CustomerID" 
      ControlID="DropDownList1" PropertyName="SelectedValue"  
      DefaultValue="-1" />
  

  Then in your SQL statement, check for that same default value from your ControlParameter:

   SELECT * 
   FROM Invoices
   WHERE (CustomerID = @CustomerID OR @CustomerID = -1)
  

  Germ : @pcampbell: great answer, we think alike

• How would this work with Multiple Optional Parameters?