在asp.net中点击[show]按钮，从数据库中选择dropdownlist中的选项，如何填充其他dropdownlist？

protected void ShowButton_Click(object sender, EventArgs e)
{
    // 连接数据库，执行查询操作，获取数据
    string connectionString = "YourConnectionString";
    SqlConnection connection = new SqlConnection(connectionString);
    SqlCommand command = new SqlCommand("SELECT * FROM YourTable", connection);
    SqlDataAdapter adapter = new SqlDataAdapter(command);
    DataTable dataTable = new DataTable();
    adapter.Fill(dataTable);

    // 将数据绑定到第一个dropdownlist
    DropDownList1.DataSource = dataTable;
    DropDownList1.DataTextField = "ColumnName";
    DropDownList1.DataValueField = "ColumnValue";
    DropDownList1.DataBind();
}

protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e)
{
    // 获取第一个dropdownlist的选中项的值
    string selectedValue = DropDownList1.SelectedValue;

    // 根据选中项的值查询相关数据
    string connectionString = "YourConnectionString";
    SqlConnection connection = new SqlConnection(connectionString);
    SqlCommand command = new SqlCommand("SELECT * FROM YourTable WHERE ColumnValue = @SelectedValue", connection);
    command.Parameters.AddWithValue("@SelectedValue", selectedValue);
    SqlDataAdapter adapter = new SqlDataAdapter(command);
    DataTable dataTable = new DataTable();
    adapter.Fill(dataTable);

    // 将查询到的数据绑定到第二个dropdownlist
    DropDownList2.DataSource = dataTable;
    DropDownList2.DataTextField = "ColumnName";
    DropDownList2.DataValueField = "ColumnValue";
    DropDownList2.DataBind();
}