SqlDataReader dataReader = datacommand.ExecuteReader();

            string productId = null;
            string unitprice = null;
            string quantity = null;

            if (dataReader.Read())
            {
                productId = dataReader.GetString(1);
                unitprice = dataReader.GetDecimal(2).ToString();
                quantity = dataReader.GetInt16(3).ToString();
            }
            else
            {
                MessageBox.Show("找不到任何记录", "出错啦");
                textBox1.Text = "";
            }

            textBox2.Text = productId;
            textBox3.Text = unitprice;
            textBox4.Text = quantity;