public void consultar(string sql)
        {
            MySqlConnection conexion = new MySqlConnection();
            conexion.ConnectionString = "SERVER=192.168.0.215;Database=agenda; Uid=Alumnos;Pwd=1234;";
            conexion.Open();


            MySqlCommand cmd = new MySqlCommand(sql, conexion);
            MySqlDataAdapter da = new MySqlDataAdapter(cmd);
            DataTable dt = new DataTable();
            da.Fill(dt);
            dataGridView1.DataSource = dt;
            conexion.Close();
        }