SqlCommandBuilder 报错

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 test1
{
    public partial class Form1 : Form
    {
        private static DataSet dataSet = new DataSet();
        private static SqlDataAdapter dataAdapter;

        public Form1()
        {
            InitializeComponent();
        }
        private void stand()
        {
            string sql = "select name,address from a ";
            dataAdapter = new SqlDataAdapter(sql, DBHelper.connection);
            dataAdapter.Fill(dataSet,"test");
            dataGridView1.DataSource = dataSet.Tables["test"];


        }

        private void button2_Click(object sender, EventArgs e)
        {
            this.Close();
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            stand();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            /*dataSet.Tables["test"].Clear();
            string sql = "select name,address,statue from a ";
            switch (comboBox1.Text)
            {
                case "1":
                     sql=sql+" where statue=1";
                    break;
                case "2":
                    sql = sql + " where statue=2";
                    break;
                case "4":
                    sql = sql + " where statue=4";
                    break;
                default:
                    break;}
                    dataAdapter.SelectCommand.CommandText = sql;
                    dataAdapter.Fill(dataSet,"test");
                    //dataGridView1.DataSource = dataSet.Tables["test"];
            */
        }

        private void button3_Click(object sender, EventArgs e)
        {

            try
            {

                SqlCommandBuilder builder = new SqlCommandBuilder(dataAdapter);
               dataAdapter.Update(dataSet,"test");
            }
            catch(Exception ex)
            {
                MessageBox.Show(ex.Message);
            }
        }
    }
}
运行到dataAdapter.Update(dataSet,"test");报错

Dynamic SQL generation for the UpdateCommand is not supported against a SelectCommand that does not return any key column information.
之前没遇到这错误。我看了写法也没错。不知道哪里出错了
--------------------编程问答-------------------- dataAdapter.Update(dataSet,"test"); //很明显这个dataset是空的！！
--------------------编程问答-------------------- 怎么是空的？不是Fill了吗？
string sql = "select name,address from a ";
            dataAdapter = new SqlDataAdapter(sql, DBHelper.connection);
            dataAdapter.Fill(dataSet,"test");
            dataGridView1.DataSource = dataSet.Tables["test"];
--------------------编程问答-------------------- 为UPDATECOMMAND动态生成的SQL语句不支持不返回包含主键字段信息的SELECTCOMMAND属性，SELECTCOMMAND属性的执行结果中所获取的字段必须包含主键，也就是数据库必须要有一个字段作为主键
主键必需 --------------------编程问答-------------------- Dynamic SQL generation for the UpdateCommand is not supported against a SelectCommand that does not return any key column information.
之前没遇到这错误。我看了写法也没错。不知道哪里出错了

很明显的提示说,

更新语句不支持查询SelectCommand 不返回任何键列信息

你的表没有主键

补充：.NET技术 ,  C#