public void userSales()
{
    con.Open();

    SqlCommand cmd = new SqlCommand("SELECT SalesActivity.Activity_ID, SalesActivity.Date, SalesActivity.Quatation_Number, CUSTOMER.Customer_Name, PRODUCTS.Machine_Model, SalesActivity.Quantity, SalesActivity.valueGBR, SalesActivity.valueEUR, SalesActivity.Rate, SalesActivity.weightedValue, STATUS.Status, SalesActivity.estDecisionDate, SalesActivity.PromisedDeliveryDate FROM SalesActivity INNER JOIN CUSTOMER ON SalesActivity.Customer_ID = CUSTOMER.Customer_ID INNER JOIN PRODUCTS ON SalesActivity.Product_ID = PRODUCTS.Product_ID INNER JOIN STATUS ON SalesActivity.Status_ID = STATUS.Status_ID ", con);
    SqlDataAdapter da = new SqlDataAdapter(cmd);
    DataSet ds = new DataSet();
    da.Fill(ds);
    con.Close();

    if (ds.Tables[0].Rows.Count > 0)
    {
        GridView1.DataSource = ds;
        GridView1.DataBind();
    }
    else
    {
        ds.Tables[0].Rows.Add(ds.Tables[0].NewRow());  // if record not found then returning a blank table structure
        GridView1.DataSource = ds;
        GridView1.DataBind();

        int columncount = GridView1.Rows[0].Cells.Count;

        GridView1.Rows[0].Cells.Clear();
        GridView1.Rows[0].Cells.Add(new TableCell());
        GridView1.Rows[0].Cells[0].ColumnSpan = columncount;
        GridView1.Rows[0].Cells[0].Text = "No Records Found";
    }
}

protected void GridView1_RowEditing(object sender, GridViewEditEventArgs e)
{
    GridView1.EditIndex = e.NewEditIndex; //this open new index that is edit mode
    userSales();
}

protected void GridView1_RowCancelingEdit(object sender, GridViewCancelEditEventArgs e)
{
    GridView1.EditIndex = -1;   //after cancel button want go to one index back that's y -1
    userSales();
}

protected void GridView1_RowCommand(object sender, GridViewCommandEventArgs e)
{
    if (e.CommandName.Equals("AddNew"))
    {
        TextBox txtActivity = (TextBox)GridView1.FooterRow.FindControl("ftxtActivity");
        TextBox ftxtDate = (TextBox)GridView1.FooterRow.FindControl("ftxtDate");
        TextBox ftxtQno = (TextBox)GridView1.FooterRow.FindControl("ftxtQno");
        DropDownList fddlCName = GridView1.FooterRow.FindControl("fddlCName") as DropDownList;
        DropDownList fddlMmodel = GridView1.FooterRow.FindControl("fddlMmodel") as DropDownList;
        TextBox ftxtQuantity = (TextBox)GridView1.FooterRow.FindControl("ftxtQuantity");
        TextBox ftxtvalueGBR = (TextBox)GridView1.FooterRow.FindControl("ftxtvalueGBR");
        TextBox ftxtvalueEUR = (TextBox)GridView1.FooterRow.FindControl("ftxtvalueEUR");
        TextBox ftxtRate = (TextBox)GridView1.FooterRow.FindControl("ftxtRate");
        TextBox ftxtweightedValue = (TextBox)GridView1.FooterRow.FindControl("ftxtweightedValue");
        DropDownList fddlStatus = GridView1.FooterRow.FindControl("fddlStatus") as DropDownList;
        TextBox ftxtestDecisionDate = (TextBox)GridView1.FooterRow.FindControl("ftxtestDecisionDate");
        TextBox ftxtPromisedDeliveryDate = (TextBox)GridView1.FooterRow.FindControl("ftxtPromisedDeliveryDate");

        con.Open();

        SqlCommand cmd = new SqlCommand("INSERT INTO SalesActivity(Activity_ID, Date, Quotation_Number, Customer_Name, Machine_Model,Quantity, valueGBR, valueEUR, Rate, weightedValue, Status, estDecisionDate, PromisedDeliveryDate) VALUES(@Activity_ID, @Date, @Quotation_Number, @Customer_Name, @Machine_Model, @Quantity, @valueGBR, @valueEUR, @Rate, @weightedValue, @Status, @estDecisionDate, @PromisedDeliveryDate)", con);
        cmd.Parameters.AddWithValue("@Activity_ID", txtActivity.Text.Trim());
        cmd.Parameters.AddWithValue("@Date", ftxtDate.Text.Trim());
        cmd.Parameters.AddWithValue("@Quotation_Number", ftxtQno.Text.Trim());
        cmd.Parameters.AddWithValue("@Customer_Name", fddlCName.SelectedItem.Text);
        cmd.Parameters.AddWithValue("@Machine_Model", fddlMmodel.SelectedItem.Text);
        cmd.Parameters.AddWithValue("@Quantity",  ftxtQuantity.Text.Trim());
        cmd.Parameters.AddWithValue("@valueGBR", ftxtvalueGBR.Text.Trim());
        cmd.Parameters.AddWithValue("@valueEUR",  ftxtvalueEUR.Text.Trim());
        cmd.Parameters.AddWithValue("@weightedValue",ftxtweightedValue.Text.Trim());
        cmd.Parameters.AddWithValue("@Rate",  ftxtRate.Text.Trim());
        cmd.Parameters.AddWithValue("@Status",  fddlStatus.SelectedItem.Text);
        cmd.Parameters.AddWithValue("@estDecisionDate", ftxtestDecisionDate.Text.Trim());
        cmd.Parameters.AddWithValue("@PromisedDeliveryDate", ftxtPromisedDeliveryDate.Text.Trim());

        int result = cmd.ExecuteNonQuery();

        con.Close();

        if (result == 1)
        {
            userSales();
            Response.Write("<script language=javascript>alert('" + txtActivity.Text + "'+'Sale Details inserted successfully');</script>");
        }
        else
        {
            Response.Write("<script language=javascript>alert('" + txtActivity.Text + "'+' Sale Details not inserted');</script>");
        }
    }
}

SELECT SalesActivity.Activity_ID
    ,SalesActivity.DATE
    ,SalesActivity.Quatation_Number
    ,CUSTOMER.Customer_Name
    ,PRODUCTS.Machine_Model
    ,SalesActivity.Quantity
    ,SalesActivity.valueGBR
    ,SalesActivity.valueEUR
    ,SalesActivity.Rate
    ,SalesActivity.weightedValue
    ,STATUS.STATUS
    ,SalesActivity.estDecisionDate
    ,SalesActivity.PromisedDeliveryDate
FROM SalesActivity
INNER JOIN CUSTOMER ON SalesActivity.Customer_ID = CUSTOMER.Customer_ID
INNER JOIN PRODUCTS ON SalesActivity.Product_ID = PRODUCTS.Product_ID
INNER JOIN STATUS ON SalesActivity.Status_ID = STATUS.Status_ID