面向对象select方法

<?php

class Table{
         protected $tablename;
         protected $arrTable;
        protected $w='';//条件属性
        protected $field="*";//查询字段
        protected $order="";
         function __construct($arrTable=''){
               $this->tablename=get_class($this);//获取获取当前的对象名
                $this->arrTable=$arrTable;
         }
         function insert(){
                echo $this->insertTable();
             }
         private function insertTable(){
             $keys="(";
             $values="(";
             foreach ($this->arrTable as $key => $value) {
                $keys.=$key.",";
                $values.="'".$value."',";
             }
             $keys=substr($keys, 0,-1).")";
             $values=substr($values,0,-1).")";
             return  "insert {$this->tablename} {$keys} values {$values}<br>";
          }

function del(){
            if ($this->w!=''){//表示没有条件
               $delstr="delete from {$this->tablename} where {$this->w}";               
            }else{
               $delstr="delete from {$this->tablename}";
            }
            echo $delstr."<br>";

}
         function where($w=''){
            $this->w=$w;
         }
          function update(){
            $updateData="";
            foreach ($this->arrTable as $key => $value) {
                $updateData.=$key."=".$value.",";
            }
            $updateData=substr($updateData,0,-1);
            if ($this->w=="") {
               echo "update {$this->tablename} set {$updateData} <br>";
            }else{
               echo "update {$this->tablename} set {$updateData} where {$this->w}<br>";
            }
            
         }
          function select(){
            if ($this->w==""){
               $select="select {$this->field} from {$this->tablename} {$this->order}";  
            }else{
               $select="select {$this->field} from {$this->tablename} where {$this->w} {$this->order}";  
            }
            echo $select."<br>";

}
         //查询字段
         function field($field="*"){
            $this->field=$field;
         }
         //排序
         function order($order=''){
            $this->order=$order;
         }
   }
   /**
   *
   */
   class User extends Table
   {
         
       
   }
   /**
   *
   */
   class Article extends Table
   {
       
       
   }
   /**
   *
   */
   class Student extends Table
   {
      
     
   }
   $Datas=array("username"=>"admin","userpass"=>'admin');
   $user1=new User($Datas);
   $user1->insert();
   $Datas=array("title"=>"admin","author"=>'admin');
   $a=new Article($Datas);
   $a->insert();
   $a->where("title='清远'");
   $a->del();
   $a->update();
   $Datas = array('id' =>'001' ,'name'=>'zhangsan' );
   $s1=new Student($Datas);
   $s1->insert();
   $s1->field("title,author");
   $s1->select();

// $iswhere=""

?>