private void txtDongia_TextChanged(object sender, EventArgs e) { double dg = Convert.ToDouble(DAO.Docbang("SELECT DONGIANHAP FROM DM_HANG_HOA WHERE MAVACH = N'" + txtMavach.Text + "'").Rows[0][0].ToString()); double gnmoi = dg + Convert.ToDouble(txtDongia.Text); string sql; sql = "UPDATE DM_HANG_HOA SET DONGIANHAP=" + gnmoi + "WHERE MAVACH = N'" + txtMavach.Text + "'"; DAO.RunSQL(sql); }