<?php   class DBHelper{    private $mysqli;    private static $host=‘127.0.0.1‘;    private static $user=‘root‘;    private static $pwd=‘‘;    private static $dbname=‘‘;        //通过构造方法进行初始化操作    public function __construct(){        $this->mysqli=new mysqli(self::$host,self::$user,self::$pwd,self::$dbname)        or die(‘数据库链接出错:‘.$this->mysqli->connect_error);            //设置数据库编码为utf8        $this->mysqli->query(‘set names utf8‘);        }        //执行查询语句    public function execute_dml($sql){        $arr=array();        $result=$this->mysqli->query($sql) or die($this->mysqli->error);        if($result){        while($row=$result->fetch_assoc()){            //将查询结果封装到一个数组中，返回给方法调用处            $arr[]=$row;        }            //释放查询结果资源        $result->free();        }            return $arr;    }    //执行统计语句    public function total($sql){        $result = $this->mysqli->query($sql) or die($this->mysqli->error);        return $result->num_rows;     }        //执行增加、删除、更新语句    public function execute_dql($sql){        $result=$this->mysqli->query($sql) or die($this->mysqli->error);        if(!$result){        return 0;//表示操作失败            }else{        if($this->mysqli->affected_rows>0){            return 1;//操作成功            }else{            return 2;//没有受影响的行            }        }    }    }?>