private void cbo_MaThuoc_SelectedIndexChanged(object sender, EventArgs e) { string strsel = "select GiaBan from Thuoc where TenThuoc LIKE N'%" + cbo_MaThuoc.Text.Trim() + "%'"; SqlDataReader dr = conn.excuteReader(strsel); while (dr.Read()) { txt_DonGia.Text = dr["GiaBan"].ToString(); } dr.Close(); conn.ClosedConnection(); }