Laravel 5.2 - 在子查询上使用左连接时出现奇怪的结果

I have the following query:

我有以下查询：

$products = Product::leftJoin(DB::Raw('(SELECT imageable_id, MIN(created_at) as min_created_at
                               FROM images WHERE imageable_type = "App\\Product"
                               GROUP BY imageable_id) AS subquery'), function($join)  {
                                $join->on('subquery.imageable_id', '=', 'products.id');
                        })
                        ->leftJoin('images', function ($join) {
                            $join->on('images.imageable_id', '=', 'subquery.imageable_id')
                                ->where('images.created_at', '=', 'subquery.min_created_at');})
                       ->select('products.*', 'images.file_path')
                       ->paginate(5);
$produc