private void button1_Click(object sender, EventArgs e)
        {
            String exeStr = "DELETE FROM ReturnedHistory ";

            new Class_CRUDdb().exeData(exeStr);
            Form_Statistics.refeshLichsuTraSach();
        }
 private void button2_Click_1(object sender, EventArgs e)
 {
     //statics
     ColorClear();
     button2.BackColor = Color.CadetBlue;
     form_Statistics1.BringToFront();
     Form_Statistics.refeshSachDaMuon();
     Form_Statistics.refeshLichsuTraSach();
     Form_Statistics.refeshSinhvienQuahan();
 }