<?php
$Pid = '50025';
//找出3级
for ($i = 1; $i < 3;) {
   $where = array();
   $where['id'] = $Pid;
   $field = 'l_id,id';
   $vo = M("User")->where($where)->field($field)->find();
   if ($vo) {
      $Fid = $vo['l_id'];
   } else {
      break;
   }
   if ($Fid > 0) {
      $Pid = $Fid;
      var_dump($Pid);
      $i++;
   } else {
      break;
   }
}
?>