自己写的简易数据库类

 class mysql{
      private $host;
   private $username;
   private $password;
   private $dbname;
   private $charset='utf8';
   public $conn;

  public function __construct($host='localhost',$username='root',$password="",$dbname='test'){
      $this->host=$host;
   $this->username=$username;
   $this->password=$password;
   $this->conn=mysql_connect($this->host,$this->username,$this->password);
   $this->query('set names '.$this->charset);
   $this->selectdb($dbname);
   }
   //执行sql语句
   public function  query($sql){
   $res=mysql_query($sql);
   return $res;
   }
       //选择数据库
  private function selectdb($dbname){
     $this->dbname=$dbname;
     $this->query('use '.$this->dbname);
  }
       //返回多行记录的数组
  function getList($sql){
     $res=$this->query($sql);
    
     $list=array();
     while($row=mysql_fetch_assoc($res)){
        $list[]=$row;
     }
    // var_dump($list);
     return $list;
  }
       //返回一行记录
  function getRow($sql){
    $res=$this->query($sql);
    $row=mysql_fetch_assoc($res); 
    return $row;
  }
  function __destruct(){
    mysql_close();
  }
  //按照数组$arr=array(key=>value),key为字段，value为值的形式插入数据到goods（数据库练习的那张goods）表中
  function insert($arr){
   $value="";
   foreach($arr as $list){
      if(is_string($list)){//判断数组的值是否为字符串
         $value.="'".$list."',";//是字符串加上引号
      }else{
         $value.=$list;
      }
   }
     $value=trim($value);
   
  
     $field=implode(',',array_keys($arr));//取得键值作为字段
     $sql="insert into goods(".$field.") values(".$value.")";
     echo $sql;
    if( $this->query($sql)){
     echo '插入数据成功';
    }else{
     echo mysql_error();
    }
  }
     //返回单个值
    function getOne($sql){
       $res=$this->query($sql);
    $row=mysql_fetch_row($res);
    return $row[0];
     }
  
   }
 
//   $my=new mysql();
//   $my->selectdb('test');
//   $arr=array('goods_name'=>'lisi','cat_id'=>3);
//   $my->insert($arr);