更新dataGridView中的数据到数据库文件中

Question

看MSDN示例也看了半天了，自己的就是不成功。以下是代码，挺简单的

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

namespace StudentStatusManagementSystem.Admin
{
    public partial class AdminManage : Form
    {
        private DataTable dt = new DataTable();
        private SqlDataAdapter sda = new SqlDataAdapter(); 
        public AdminManage()
        {
            InitializeComponent();
            

        }

        private void AdminManage_Load(object sender, EventArgs e)
        {


            SqlConnection conn = new SqlConnection(Properties.Settings.Default.DatabaseConnectionString);
            SqlCommand scd = new SqlCommand("select * from Student", conn);
            sda.SelectCommand = scd;
            sda.Fill(dt);
            dataGridView.DataSource = dt; 
        }

        SqlCommandBuilder scb = new SqlCommandBuilder();

        private void 保存SToolStripButton_Click(object sender, EventArgs e)
        {
            
            try
            {
                this.Validate();
                this.studentBindingSource.EndEdit();
                SqlCommandBuilder scb = new SqlCommandBuilder(sda);
                sda.Update(dt);
            }
            catch (System.Exception ex)
            {
                MessageBox.Show(ex.ToString());
                return;
            }
            MessageBox.Show("更新成功!");
            //studentTableAdapter.Update(this.databaseDataSet.Student);

           
        }

    }
}

数据能正确读出来并显示出来，但是就是更新不了数据啊！代码运行也没问题，一切正常但是数据库里的数据就是不变！！！

求高人解答！！！