递归-子孙树

    //子孙树-查出所有的商品分类
    public function gettree( $cat_id = 0 ,$lv = 0 ){//lv辅助统计第几级分类
        $tree = array();
        $cat = select * form table_cat;
        foreach($cat as $k=>$v){
            if($v['parent_id'] == $cat_id){
                $v['lv'] = $lv;
                $tree[] = $v;
                //检查是否有子栏目
                $tree = array_merge($tree,$this->gettree($v['cat_id'],$lv+1));//array_merge合并数组
            }
        }
        return $tree;
    }