public function get_data($limit){
 $sql="select * from ((select id,name from `mytable` limit {$limit},10) union all (select id,name from `mytable` limit 0,10)) as test limit 0,10";
　　  return $this->query($sql);
 }

 public function getCount(){//获取数据的条数
     $sql="select count(id) as t from `mytable`";
     return $this->query($sql);
 }

//测试数据库无限循环取数据
   public function getInfiniteData(){
    //用户点击数
    $page = $_GET['click'];
　　　　 //每次展示条数
    $pagesize = 10;
　　　　　//获取总条数
    $total = $this->Mydemo->get_count();
    $t = $total[0][0]['t'];
　　　　　//算出每次点击的其起始位置
    $limit = (($page - 1)*$pagesize)%$t;
    $data = $this->Mydemo->get_data($limit);
    if (!empty($data)) {
      //转换为二维数组
      $list = [];
      foreach ($data as $key => $v) {
        $list[$key] = $data[$key][0];
      }
      $info['msg'] = $list;
      $info['code'] = '001';
    }else{
      $info['code'] = '002';
      $info['msg'] = '暂无数据';
    }
    echo json_encode($info,JSON_UNESCAPED_UNICODE);die;
  }