1. set strict to false in config/databtase.php
2. ->select([
'exam_registrations.id',
'exam_registrations.exam_id',
'exam_registrations.user_id',
DB::raw('sum(submissions.marks) as totalMarksGained')
])
->groupBy('exam_registrations.user_id')
->orderBy('totalMarksGained', 'DESC')