这就像将标准文本框值保存到数据库中一样。

有关保存到数据库的标准教程，请通过 -

将文本框中的数据保存到asp.net中的数据库 [ ^ ]

如何在asp.net中将数据插入数据库 [ ^ ]



有关下拉列表的具体示例 -

选中后，从下拉列表中保存数据库中的多个选定列表项 [ ^ ]

This is to be done just like you would save a standard textbox value into the database.
For standard tutorials on saving to database, go through -
Save data from textboxes to database in asp.net [^]
How to Insert data into database in asp net [^]

For specific example on dropdowns -
Save multiple selected list items in database from dropdown list when selected[^]

protected void Page_Init(object sender, EventArgs e)
    {
       
        if (!IsPostBack)
        {
            FillCountry();
           
        }
    }
 public void FillCountry()
    {
        cn.Open();
        cmd.Connection = cn;
        cmd.CommandText = "Select ID, Countries from Countries";
        SqlDataReader dr = cmd.ExecuteReader();
        Country.Items.Clear();
        Country.DataSource = dr;
        Country.DataTextField = "Countries";
        Country.DataValueField = "ID";
        Country.DataBind();
        Country.Items.Insert(0, "--Select--");
        cn.Close();
        cmd.Dispose();
    }

    public void FillStates()
    {

        if (Page.IsPostBack)
        {
            cn.Open();
            cmd.Connection = cn;
            cmd.CommandText = "Select StateID, States from States where CountryId = '" + Country.SelectedValue + "'";
            SqlDataReader dr = cmd.ExecuteReader();
            State.Items.Clear();
            State.DataSource = dr;
            State.DataTextField = "States";
            State.DataValueField = "StateID";
            State.DataBind();
            State.Items.Insert(0, "--Select--");
            cn.Close();
            cmd.Dispose();

        }
    }



    protected void Country_SelectedIndexChanged(object sender, EventArgs e)
    {
        FillStates();
    }
}