尝试类似下面的方法。

$results = Clockin::select('clockin.working_day as cdate', 'clockin.*', 'sch_week.*', 'user.schedule_id', 'user.username', 
                DB::raw("(SELECT GROUP_CONCAT(time separator '==') from clockin WHERE employee_no=user.employee_no AND working_day=cdate GROUP by working_day ) as time"))
            ->join('user_personal as user', 'user.employee_no', '=', 'clockin.employee_no')
            ->join('schedule_week as sch_week', function($join) {
                $join->on('user.schedule_id', '=', 'sch_week.schedule_id')
                     ->on(DB::raw("week_day = date_format(working_day,'%a')"));
            })
            ->whereMonth('working_day', Carbon::now()->month)
            ->groupBy('user.employee_no', 'clockin.working_day')
            ->orderBy('clockin.working_day', 'desc')
            ->orderBy('user.employee_no')
            ->get();