public function join(){
//用于监听SQL
     Db::listen(function ($sql, $time, $explain) {
            // 记录SQL
            echo $sql . ‘ [‘ . $time . ‘s]<br>‘;
            // 查看性能分析结果
            //dump($explain);
      });
//$brand = Brand::all([3,4]);//未预载入  程序执行了5句SQL语句
$brand = Brand::with(‘goods‘)->select([3,4]);//预载入后  程序执行了4句SQL语句
  foreach($brand as $b){
      foreach($b->goods as $good){
          echo $good->goods_name."：".$good->price."元<br>";  
      }
  }
}    

public function join(){
  $brand = Brand::withCount(‘goods‘)->select([3,4]);
  foreach($brand as $b){
    //“方法名+_count”为系统自动生成的自动用于存储统计的值，也可自定义
    echo "品牌："$b->brand_name."有"$b->goods_count."个商品<br>":
  }
}

public function join(){
    $brand = Brand::withMax(‘good‘,‘price‘)->select();
    foreach($brand as $value){
       echo $value->brand_name"的品牌中最贵的商品价格为：".$value->goods_max;
    }
}