我的逻辑是，如果ddlCoffee.SelectedIndex = 0，则不会在我的数据库中添加任何行。我确实尝试过 sqlcmd.Parameters.AddWithValue（“ @ Qty”，（（object）ddlCoffee.SelectedIndex）?? DBNull.Value）; ，但是在SQL中它以 Qty 0 出现。我不想要的SQL数据库中的strong>值行。如果数量为0，我不想添加任何行。请告知我该怎么办？

.aspx.cs

      protected void BtnSubmit_Click(object sender,EventArgs e)
    {
        string connString = "Data Source";
        string insertCommand = "INSERT INTO tbDrinks ( DrinkName,DateOfOrder,Qty,username,UserCompany) " +
            "values(@DrinkName,@DateOfOrder,@Qty,@username,@UserCompany)";

        using (SqlConnection conn = new SqlConnection(connString))
        {
            conn.Open();
            using (SqlCommand sqlcmd = new SqlCommand(insertCommand,conn))
            {

                sqlcmd.Parameters.AddWithValue("@DrinkName",lblCoffee.Text);
                sqlcmd.Parameters.AddWithValue("@DateOfOrder",DateTime.Today);

                if (ddlCoffee.SelectedIndex != 0)
                {
                    sqlcmd.Parameters.AddWithValue("@Qty",ddlCoffee.SelectedValue);
                }
                else
                {
                    //sqlcmd.Parameters.AddWithValue("@Qty",((object)ddlCoffee.SelectedIndex) ?? DBNull.Value);
                    //Will Not Add in SQL Database
                }

                sqlcmd.Parameters.AddWithValue("@username",txtusername.Text);
                sqlcmd.Parameters.AddWithValue("@UserCompany",txtCompanyName.Text);
                sqlcmd.ExecuteNonQuery();
              }
             }
           }

.aspx

<table id="tbHotDrinks" class="auto-style3" border="1" bordercolor="#1FC3F3" runat="server">

    <tr>
        <td>
            <asp:Label ID="lblCoffee" runat="server" Text="Coffee"></asp:Label>
        </td>
        <td class="auto-style2">
            <asp:Image ID="coffee" runat="server" Height="76px" ImageUrl="~/images/coffee.gif" Width="99px" ImageAlign="TextTop" />
        </td>

        <td class="auto-style11">
            <asp:DropDownList ID="ddlCoffee" runat="server">
               <asp:ListItem Value="0">--Select Qty--</asp:ListItem>
               <asp:ListItem>1</asp:ListItem>
                <asp:ListItem>2</asp:ListItem>
                <asp:ListItem>3</asp:ListItem>
                <asp:ListItem>4</asp:ListItem>
                <asp:ListItem>5</asp:ListItem>
                <asp:ListItem>6</asp:ListItem>
                <asp:ListItem>7</asp:ListItem>
                <asp:ListItem>8</asp:ListItem>
                <asp:ListItem>9</asp:ListItem>                        
            </asp:DropDownList>

        </td>

    </tr>
</table>