<asp:TextBox ID="txtVal" runat="server" Text="1"></asp:TextBox>

        <asp:SqlDataSource ID="SqlDataSource1" runat="server" 
            ConnectionString="<%$ ConnectionStrings:stringaConnessione %>" 
            SelectCommand="SELECT anno * @val AS test FROM anni">
            <SelectParameters>
                <asp:ControlParameter 
                    ControlID="txtVal" 
                    Name="val" 
                    PropertyName="Text" 
                    DefaultValue="1" />
            </SelectParameters>
        </asp:SqlDataSource>


        <asp:GridView ID="GridView1" runat="server" DataSourceID="SqlDataSource1"></asp:GridView>