怎么看也看不出，我写的代码出了什么问题

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using System.Data.SqlClient;
namespace MyForm
{
    public partial class StudentListForm : Form
    {
        DataSet dataset = new DataSet();
        SqlDataAdapter dataAdapter;
        public StudentListForm()
        {
            InitializeComponent();
        }        private void button1_Click(object sender, EventArgs e)
        {
            
            if (comboBox1.Text == "")
            {
                MessageBox.Show("请选择查询范围！", "操作提示", MessageBoxButtons.OK, MessageBoxIcon.Information);
            }
            else
            { 
                string sql = "select stuUser,stuName,stuNo,stuSex,stuPhone from studentinfo";
                switch (comboBox1.Text)
                {
                    case "男": sql += " where stuSex='男'"; break;
                    case "女": sql += " where stuSex='女'"; break;
                    default: break;
                }
                dataset.Tables["student"].Clear();
                dataAdapter.SelectCommand.CommandText = sql;
                dataAdapter.Fill(dataset,"student");
                          }
        }        private void StudentListForm_Load(object sender, EventArgs e)
        {
            string sql = "select stuid stuUser,stuName,stuNo,stuSex,stuPhone from studentinfo";
            dataAdapter = new SqlDataAdapter(sql, DBHelper.connection);
            dataAdapter.Fill(dataset, "student");
            dataGridView1.DataSource = dataset.Tables["student"];
        }        private void button2_Click(object sender, EventArgs e)
        {
            DialogResult result = MessageBox.Show("确定要将修改保存到结果库吗？", "操作提示", MessageBoxButtons.OKCancel, MessageBoxIcon.Question);
            if (result == DialogResult.OK)
            {
                SqlCommandBuilder builder = new SqlCommandBuilder(dataAdapter);
                ///////////就这下面这条总是发生异常，不能运行
//对于不返回任何键列信息的 SelectCommand，不支持 UpdateCommand 的动态 SQL 生成。                dataAdapter.Update(dataset,"student");
            }
        }        private void button3_Click(object sender, EventArgs e)
        {
        }        private void button4_Click(object sender, EventArgs e)
        {
            this.Close();
        }    }
}
////////////////////////////////////
系统生成的写不下了