With ASP.Net 2.0, using multiple DropdownLists is really simple. However, what happens when you want to add an extra item to the first DDL, like ‘ALL’?
Consider this scenario: You want all models (in this sample) returned, when the ‘All’ item is chosen.
You can’t put 2 SelectCommands in one DataSource control, but, when ‘All’ is selected, you still need the SQL statement (in this case, the DataSource Control’s ‘SelectCommand’ property) to change.

But, with just a little code, this is still fairly easy to accomplish. To do this, in this scenario, we’ll need two DropDownLists – one for the ‘Brands’ of automobiles, and one for the ‘Models’ of the particular brands. First, you create a new sub (here, it’s named ‘doCheck’, but you can call it anything you want), and add the following code:

Sub doCheck(Source as Object, E as EventArgs)
	if ddlBrand.SelectedItem.Value=99 then
		ds2.selectCommand="Select id, model from Models order by model"
	End If
End Sub

Then, reference that subroutine in the DropDownList’s tag:

<asp:DropDownList id="ddlBrand" DataTextField="Brand" DataValueField="id"
	 DataSourceID="DS1" AppendDataBoundItems="True" Runat="server"
	  AutoPostBack="True" OnSelectedIndexChanged="doCheck"
<asp:ListItem Value="99">All</asp:ListItem>
</asp:DropDownList>

The ‘AppendDataBoundItems’ property is added, along with the ListItem, containing a value, so that the ‘All’ entry gets added to the DDL along with all the items returned from the Database. Keep in mind, the ‘All item was appended here, with a value of 99. There’s nothing magical about that number. It simply must be a number higher than anything the DDL’s databound value will return.

Next, we’ll create the second DropDownList (for the models table):

<asp:DropDownList id="ddlModels" DataTextField="Model"
 	DataValueField="id"
	DataSourceID="DS2" Runat="server">
</asp:DropDownList>

Notice that each one of the DDLs reference it’s own DataSource control (DS1, and DS2). So, let’s create them here:
Continues…