PHP での mysqli 拡張ライブラリ (オブジェクト指向ベース) の追加、削除、変更、クエリの実装方法の例の共有

<?php
 //数据库操作类
 class DBUtil{
  private $host="localhost";
  private $username="root";
  private $password="123456";
  private $dbname="student";
  private $conn;
  public function DBUtil(){
   $this->conn=new mysqli($this->host, $this->username, $this->password,$this->dbname) or die($this->conn->connect_error);
  }
 //查询
  public function query($sql){
   $all= $this->conn->query($sql);
   return $all;
  }
 //插入,修改，删除
  public function otherOperate($sql){
   if($this->conn->query($sql)){
    if($this->conn->affected_rows>0){
      return "OK";
    }else{
      return "ERROOR";
    }
   }
  }
  public function close(){
   $this->conn->close();
  }
 }
?>

<?php
 require_once "MySQLUtil.php";
  /*$sql="select * from m_student";
  $util=new DBUtil();
  $result=$util->query($sql);
  while($row=$result->fetch_assoc()){
   echo "$row[stuName]"."</br>";
  }
  $result->free();
  $util->close();*/
  $sql="update m_student set stuName=&#39;杨幂&#39; where id=3";
  $util=new DBUtil();
  $result=$util->otherOperate($sql);
  echo $result;
  $util->close();
?>