select `u`.*, count(t.empid) as totalassignedtask from `users` as `u` left join `tasks` as `t` on `t`.`empid` = `u`.`id` where `u`.`role` = 'user' group by `t`.`empid`

$allemp = DB::table('users as u')
                        ->leftJoin('tasks as t','t.empid','=','u.id')
                        ->where('u.role','=','user')
                        ->select('u.*',DB::raw('count(t.empid) as totalassignedtask'))
                        ->groupBy('t.empid')
                        ->get();

'strict' => true,

strict => false

$allemp = DB::table('users as u')
                        ->join('tasks as t','t.empid','=','u.id')
                        ->where('u.role','=','user')
                        ->select('u.id','u.name','u.email',DB::raw('count(t.empid) as totalassignedtask'))
                        ->groupBy('u.id','u.name','u.email')
                        ->orderBy('totalassignedtask', 'asc')
                        ->get();