public Query( ConnectionHandler con)
        {
            this.con = con;

            this.con.openConnection(this.con.currentconnection);
            this.cmd = new MySqlCommand();
        }
       virtual protected void button1_Click(object sender, EventArgs e)
        {

           DisplayGrid.Columns.Clear();

           con = new ConnectionHandler();

           Query quer = new Query(con);

            if (ColumnsList.CheckedItems.Count > 0) {
                List<List<string>> lis = quer.Select(TableComboBox.SelectedItem.ToString(), concatCheckedItems(), getCheckedItems());
                FillDataGridView(lis);
            }
            else { MessageBox.Show("Seleziona degli elementi"); }
        }