Laravel 5.3问题不允许在所有字段中使用groupBy

Question

Laravel 5.3问题不允许在所有字段中使用groupBy

$response = \DB::table("posts")
        ->select("posts.id", "posts.roll_no",\DB::raw("GROUP_CONCAT(tags.name) as tagsname"))
        ->leftjoin("tags",\DB::raw("FIND_IN_SET(tags.id, posts.send_to)"),">",\DB::raw("'0'"))
        ->groupBy(["posts.id", "posts.roll_no"])
        ->get();

为什么我需要在groupB中调用“ posts.id”，“ posts.roll_no”？如果-> select（“ posts.id，*”，我删除了那些会产生错误的信息，请指导谢谢