php 如何改变产品显示的顺序

　　 //产品多图排序
    public function to_forward_product_img(Request $request)
    {
        $id = $request->param('id');
        $ph_upload_img_arr = $request->param('ph_upload_img_arr');
        $res = Db::name('product')->where('product_id',$id)
        ->field('ph_upload_img_arr')->find();
        //转成数组格式
        $arr = explode(',',$res['ph_upload_img_arr']);
        //获取键值
        $key = array_search($ph_upload_img_arr,$arr);
        //改变数组的排序
        array_splice($arr, $key-1,1,...array_splice($arr, $key,1, $arr[$key-1]));
        $str_img_arr = implode(',',$arr);
        $data = Db::name('product')->where('product_id', $id) 
        ->update(['ph_upload_img_arr' => $str_img_arr]);;
        if($data>0){
            return json(['code'=>'200', 'msg'=>"操作成功"]);
        }
    }