How to set

I am new to ASP.NET and I am studying how to use VWD.

I get a question how to set the ListItem value to "ALL" so that when I select the item "All" in the dropdown list, all the records from the database can be displayed. Can anyone tell me?  Below is the line for your reference.

<asp:ListItemValue="????"Text="All"></asp:ListItem>

I know more about classic ASP. In classic ASP, usually I can use '%' (That is Value="????" above)

Thanks