The AdsQuery component supports both named and positional parameters. You must bind data to every parameter of a parameterized query prior to executing it. You can do this either using the Params property, which is a collection property indexed by parameter position, or the ParamByName method, which takes a parameter name as an argument. Both of these approaches return a TParam, which you use to assign a value to the parameter.

The AdsQuery2 component on this project's main form has the following SQL statement assigned to its SQL property:

SELECT * FROM INVOICE WHERE [Customer ID] = :cust

The parameter, named cust, is bound and the query executed from the event handler shown in the following code segment. This event handler is associated with the Show Invoices button (shown in Figure 15-2):

procedure TForm1.ShowInvoicesBtnClick(Sender: TObject);
begin
 if AdsQuery2.Active then AdsQuery2.Close;
 if ParamText.Text = '' then
 begin
   ShowMessage('Please enter a customer number');
   Exit;
 end;
 AdsQuery2.Params[0].AsInteger := StrToInt(ParamText.Text);
 AdsQuery2.Open;
 DataSource1.DataSet := AdsQuery2;
end;