SQL会保留另一个表中不存在的记录

Question

我有两张表产品和购买

Product
Item_Code   Item_Name          Packing   MRP
1           PANADOL TAB        1*200     200
2           PARACETAMOL TAB    1*50      200
3           CALPOL SYP         2*5       5
4           AUGMENTIN DROP     1*500     234
5           DISPRIN            10*60     14
6           NUBEROL FORT       5*20      245
7           PANADOL SYP        6*9       123
8           NORAN 20 CAP       1*5       765
9           CLARITEK DROP      2*9       45
10          NIVAQUIN P SYP     3*6       34

Purchase
Pur_Invoice_No  Item_Code   Pur_Item_PackQuantity
   1               1           3
   2               1           9
   2               2           3
   2               2           3
   3               1           9
   3               3           3
   3               9           3
   3               4           3
   6               4           14

现在我想从Product表和Pur_Item_PackQuantity（来自购买表的colomn）agianst Item_Name中获取所有Item_Name，但是只显示了在Purchase表中存在的Item_Name，而不是使用以下Method给出的所有item_Name。

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Data.SqlClient;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace Mateenwin
{
public partial class SumSaleQuantity : Form
{
    public SumSaleQuantity()
    {
        InitializeComponent();
        purchaseQuantity_Bind();
        PurchaseInvoice_Bind();
        PurchaseNameQuantity_Bind();
    }



    public void PurchaseNameQuantity_Bind()
    {
        string query = "SELECT Product.Item_Name,Packing,MRP,SUM(Purchase.Pur_Item_PackQuantity) FROM Product RIGHT JOIN Purchase ON Product.Item_Code = Purchase.Item_Code Group By Item_Name,MRP,Packing  ORDER BY Item_Name ";
        SqlConnection newcon = new SqlConnection("Data Source=.;Initial Catalog=mateenwin;User ID=sa;Password=123");
        SqlCommand newcommand = new SqlCommand(query, newcon);
        SqlDataAdapter dp = new SqlDataAdapter(newcommand);
        DataTable dttt = new DataTable();
        dp.Fill(dttt);
        dataGridView3.DataSource = dttt;
    }


    private void SumSaleQuantity_Load(object sender, EventArgs e)
    {

    }


}
}

请帮助解决此问题