SSRS multiple dropdown list

Hi, 

I have the table:  Employee(ID,Name,State)

I want to parameter the state in a dropodownlist:

So the dataset is :

Select ID,Name,StatefromEmployeewhereStatein(@State)

In parameters I want to select all states:

I have set the parameter value to

=join(Parameters!<param name>.Value,",")

It worls for one state at at time but not for a combination of 2 or more states.

Any solutions please.