<asp:SqlDataSource 
            ID="SqlDataSource1" 
            runat="server" 
            ConnectionString="<%$ ConnectionStrings:catalogo %>" 
            SelectCommand="SELECT * FROM [Catalogo] WHERE (([titolo] = @titolo OR @titolo IS NULL) AND ([autore] = @autore OR @autore IS NULL) AND ( [editore] = @editore OR @editore IS NULL) AND ([genere] = @genere  OR @genere IS NULL) AND ([anno] = @anno  OR @anno IS NULL) AND ([ISBN] = @ISBN OR @ISBN IS NULL))">
            <SelectParameters>
                <asp:ControlParameter ControlID="TextTitolo" Name="titolo" PropertyName="Text" 
                    Type="String" />
                <asp:ControlParameter ControlID="TextAutore" Name="autore" PropertyName="Text" 
                    Type="String" />
                
                <asp:ControlParameter ControlID="DropDownEditore" Name="editore" 
                    PropertyName="SelectedValue" Type="String" />
                
                <asp:ControlParameter ControlID="DropDownGenere" Name="genere" 
                    PropertyName="SelectedValue" Type="String" />
                
                <asp:ControlParameter ControlID="DropDownAnno" Name="anno" 
                    PropertyName="SelectedValue" Type="String" />
                
                <asp:ControlParameter ControlID="TextISBN" Name="ISBN" PropertyName="Text" 
                    Type="String" />
            </SelectParameters>
        </asp:SqlDataSource>