How to use SqlDataSource for filling combobox as well as datatable or Dataset

Question

I am trying to fetch a column value from a datasource when some value is selected from a dropdownlist on its change event.

                <asp:DropDownList ID="ddlCityName"  runat="server" DataSourceID="dsCity" 
                    DataTextField="CityName" DataValueField="CityID" AutoPostBack="True"
                    OnTextChanged="CityName_OnTextChanged">
                </asp:DropDownList>

                <asp:SqlDataSource ID="dsCity" runat="server" 
                    ConnectionString="<%$ ConnectionStrings:GmapConnectionString %>" 
                    SelectCommand="SELECT * FROM [vcity]"
                    ></asp:SqlDataSource>

Here I want to fetch any other column's value that is not binded to a ddlCityName from sqldatasource.

I have four columns in datasource i.e. name, id, address, phno.

I want to fetch an address of a person who selects some value from ddl.