What Value Needs To Be Passed To Parameter In WHERE To Negate The Filtering

I am using two drop downs, like so:

<asp:DropDownList ID="ChurchStateDrop" runat="server"
                             DataSourceID="ChurchStateDropData" DataTextField="State"
                             DataValueField="State" AutoPostBack="True"
                             onselectedindexchanged="ChurchStateDrop_SelectedIndexChanged"
                             AppendDataBoundItems="True">
        <asp:ListItem Value="?????" Selected="True" Text="All States" />
</asp:DropDownList>

<asp:DropDownList ID="ChurchCityDrop" runat="server"
                             DataSourceID="ChurchCityDropData" DataTextField="City"
                             DataValueField="City" AutoPostBack="True"
                             onselectedindexchanged="ChurchCityDrop_SelectedIndexChanged"
                             AppendDataBoundItems="True">
        <asp:ListItem Value="?????" Selected="True"  Text="All Cities" />
</asp:DropDownList>

I have ????? in the value fields because I don't know what value needs to be passed to negate filtering (to choose all). The Dropdowns have the following SQLDatasources:<asp:SqlDataSource ID="ChurchStateDropData" runat="server"
                               ConnectionString="<%$ ConnectionStrings:tceDatabaseOnlineSQLConnection %>"
                               SelectCommand="SELECT DISTINCT
                                                                        [State]
                                                             FROM [ChurchView]"
                               DataSourceMode="DataReader">
</asp:SqlDataSource>

<asp:SqlDataSource ID="ChurchCityDropData" runat="server"
                               ConnectionString="<%$ ConnectionStrings:tceDatabaseOnlineSQLConnection %>"
                               SelectCommand="SELECT DISTINCT
                                                                        [City]
                                                             FROM [ChurchView]
                                                          WHERE ([State] = @State)"
                               DataSourceMode="DataReader">
                               <SelectParameters>
                                 <asp:ControlParameter ControlID="ChurchStateDrop"
                                                                   Name="State" PropertyName="SelectedValue" Type="String" />
                               </SelectParameters>
</asp:SqlDataSource>

Now, lets say I wanted to pass a value to the WHERE statement in ChurchCityDropData to coincide with 'All States', what would I replace value="??????" with? Now you may think I'm crazy to do such a thing, but this actually has to do with adding a Denomination Dropdown to show Denominations from all states or all cities. I will figure out the best logic for that later, I just want to know the wildcard to pass to the parameter to choose all states (negate filtering).