How to add subqueries in eloquent db of laravel 5?

I am building an api in laravel 5.3 using eloquent . if i use /api/location/event_name/event_status then i am getting results . But if i use /api/location/event_name or /api/location/ then nothing comes.how to write the query so that all my link show result . This is the code :->

class events_api extends Controller
{
      public function events($location = "",$event_name="",$event_status="")
    {

$events = DB::table('event_table')
            ->join('event_details', 'event_table.event_id', '=', 'event_details.event_id')
            ->join('venue', 'event_details.venue_id', '=', 'venue.venue_id')
            ->where('venue.venue_city','=',$location)
            ->where('event_table.event_name','=','$event_name')
            ->where('event_table.event_status','=','$event_status')
            ->where('event_table.event_post_status','=','publish')
  ->select('event_table.event_title','event_details.event_start_ts','event_details.event_views','venue.venue_name','venue.venue_city','venue.venue_location')
            ->get();

           echo $events;
    }
}``

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