procedure TForm1.Edit1KeyPress(Sender: TObject; var Key: Char);
begin
  if (Key = #13) and (Edit1.Text <> '') then
  begin
    ADOQuery1.SQL.Clear;
    ADOQuery1.SQL.Add('select count(*) from SO where SO_NO = '''   Edit1.Text   '''');
    ADOQuery1.Open;
    if ADOQuery1.Fields[0].AsInteger = 0 then
    begin
      ShowMessage('無此單號: '   Edit1.Text);
    end
    else
      ......
  end;
end;    

begin
  if Key = #13 then
    begin
      if Trim(Edit1.Text) = '' then
        ShowMessage('請輸入訂單號碼')
      else
        begin
          //以下的ADOTable1為連接SO資料表的資料集元件﹐并已Open
          if Not ADOTable1.Locate('SO_NO', Edit1.Text, [loCaseInsensitive]) then
            ShowMessage('無此單號');
        end;
    end;
end;

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