private void LoadInfoHoaDon()
{
string str;
str = "SELECT MaNV FROM tbHoaDon WHERE MaHD = '" + txtMaHD.Text + "'";
coBMaNV.Text = ConnectToSQL.GetFieldValues(str);
str = "SELECT MaKH FROM tbHoaDon WHERE MaHD = '" + txtMaHD.Text + "'";
txtMaKH.Text = ConnectToSQL.GetFieldValues(str);
str = "SELECT TenNhanVien FROM tbNhanVien WHERE MaNV = '" + coBMaNV.Text + "'";
txtTenNV.Text = ConnectToSQL.GetFieldValues(str);
str = "SELECT TenKhachHang FROM tbKhachHang WHERE MaKH = '" + txtMaKH.Text + "'";
txtTenKH.Text = ConnectToSQL.GetFieldValues(str);
str = "SELECT DiaChi FROM tbKhachHang WHERE MaKH = '" + txtMaKH.Text + "'";
txtDiaChi.Text = ConnectToSQL.GetFieldValues(str);
str = "SELECT SDT FROM tbKhachHang WHERE MaKH = '" + txtMaKH.Text + "'";
txtSdt.Text = ConnectToSQL.GetFieldValues(str);
str = "SELECT TongThanhTien FROM tbHoaDon WHERE MaHD = '" + txtMaHD.Text + "'";
txtTongThanhTien.Text = ConnectToSQL.GetFieldValues(str);
}