ช่วยดู code ให้ หน่อยคะ ไม่ทราบว่า ผิดบรรทักไหน error ขึ้นว่า Incorrect syntax near the keyword 'AS'.

private void GetData()
        {

            sb = new StringBuilder();
            sb.Remove(0, sb.Length);


            sb.Append("SELECT ");
            sb.Append("ProductId, ");
            sb.Append("ProductName, ");

            //Start***ผลรวม สินค้าในคลัง

            //   (ปรับยอด)+(รับเข้า)-(เบิก)
            sb.Append("( ");

            sb.Append("( ");
            sb.Append("ISNULL((SELECT SUM (AmountProduct) FROM [Quatation List] WHERE ProductId = Product.ProductId ");
            sb.Append("),0 ) ");
            sb.Append("+ ");

            sb.Append("( ");
            sb.Append("ISNULL((SELECT SUM([Receive Product].QuatityProduct) FROM [Receive Product] INNER JOIN [Receive] ON  ");
            sb.Append("[Receive Product].ReceiveId = [Receive].ReceiveId WHERE [Receive Product].ProductId = Product.ProductId  ");
            sb.Append("),0 ) ");
            sb.Append(" - ");

            sb.Append("( ");
            sb.Append("ISNULL((SELECT SUM([Issue Product List].AmountIssueProduct) FROM [Issue Product List] INNER JOIN [Issue Product] ON  ");
            sb.Append("[Issue Product List].IssueId = [Issue Product].IssueId WHERE [Issue Product List].ProductId = Product.ProductId  ");
            sb.Append("),0 ) ");

            sb.Append(")");
            sb.Append(" AS  Quantity ");
            sb.Append(",Unit.UnitName ");

            sb.Append(" FROM Product LEFT JOIN ");
            sb.Append("Unit ON Product.ProductId = Unit.ProductId ");

            string sqlProduct = sb.ToString();

            com = new SqlCommand();

            com.Parameters.Clear();
            com.CommandText = sqlProduct;
            com.CommandType = CommandType.Text;
            com.Connection = Conn;

            dr = com.ExecuteReader();
            if (dr.HasRows)
            {
                DataTable dtPoHard = new DataTable();
                dtPoHard.Load(dr);
                CheckResult = dtPoHard.Rows.Count;

                dgvOrder.DataSource = dtPoHard;
                HeadData();



            }
            else
            {
                CheckResult = 0;
                dgvOrder.DataSource = null;

            }
            lblCheckProduct.Text = "พบ : " + CheckResult.ToString() + " รายการ";
            dr.Close();
        }