public partial class Form1 : Form
    {
        string connString = System.Configuration.ConfigurationManager.ConnectionStrings["conn"].ToString();
          
        string sql = "select * from tab1";
        DataSet ds = new DataSet();
        public Form1()
        {
            InitializeComponent();
        }
        private void Form1_Load(object sender, EventArgs e)
        {          
            SqlConnection conn = new SqlConnection(connString);
            SqlDataAdapter ada = new SqlDataAdapter(sql, conn);
            ada.Fill(ds);
            dataGridView1.DataSource = ds.Tables[0];
          
        }      
        private void button1_Click(object sender, EventArgs e)
        {
            SqlConnection conn = new SqlConnection(connString);
            SqlDataAdapter ada = new SqlDataAdapter(sql, conn);
            SqlCommandBuilder cb = new SqlCommandBuilder(ada);
            ada.Update(ds);
            dataGridView1.Update();
        }
    
    }