or try pluck in laravelhere
DB::table('user') ->select('id','name') ->whereNotIn('id', DB::table('curses')->where('id_user', '=', $id)->pluck('user_id')) ->get();
or try pluck in laravelhere
DB::table('user') ->select('id','name') ->whereNotIn('id', DB::table('curses')->where('id_user', '=', $id)->pluck('user_id')) ->get();