c# 在datagridview修改添加数据

表student一定要设置主键，否则会出错

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Data.SqlClient;
namespace database
{
public partial class Form1 : Form
{

public DataSet myds=new DataSet();
SqlDataAdapter myda = new SqlDataAdapter("select * from student", "server=LENOVO-1389D547;database=master;uid=sa;pwd=8233");
public Form1()
{
InitializeComponent();

myda.Fill(myds, "stu");
dataGridView1.DataSource = myds.Tables["stu"];

}

private void btn1_Click(object sender, EventArgs e)
{

DataTable dtshow = (DataTable)dataGridView1.DataSource;
SqlCommandBuilder builder = new SqlCommandBuilder(myda);
this.myda.Update(dtshow);
MessageBox.Show("修改成功");

}
}
}