QueryString - Display all entries when parameter isn't specified

Question

I am using Visual Studio and C#, and I have a DataList that displays games from a database I have. I'm using QueryString to determines which genre (category) I want to display.

The DataList is populated with the game title and image, and my SqlDataSource looks like this:

<asp:sqldatasource id="SqlDataSourceGames" runat="server" connectionstring="<%$ ConnectionStrings:gamesconstring %>"
    selectcommand="SELECT uname, uimg
                    FROM games 
                    INNER JOIN categories_games
                    ON games.uid = categories_games.uid
                    INNER JOIN consoles_games
                    ON games.uid = consoles_games.uid
                    WHERE consoleid = 2
                    AND categoryid = @categoryid">
    <SelectParameters>
        <asp:QueryStringParameter Name="categoryid" DbType ="String" Direction="Input" QueryStringField="categoryid" DefaultValue="" ConvertEmptyStringToNull="true" />   
    </SelectParameters>
</asp:sqldatasource>

This works fine, and I can specify the genre by entering something like localhost/PS4.aspx?categoryid=1. However, I want to display ALL genres if the categoryid is not specified. In other words, when I go to localhost/PS4.aspx.

I tried using CancelSelectOnNullParameter="false" , that did nothing.

Answer 1

Use

...    
selectcommand="SELECT uname, uimg
                FROM games 
                INNER JOIN categories_games
                ON games.uid = categories_games.uid
                INNER JOIN consoles_games
                ON games.uid = consoles_games.uid
                WHERE consoleid = 2
                AND (categoryid = @categoryid OR @categoryid IS NULL)"

CancelSelectOnNullParameter="false">