DQL: Why Dgraph groupby query slow?

Users Dgraph
1 
{ var(func: type(UserExamLogs))@filter(eq(uxl_is_attempted,true) and eq(uxl_is_correct,true))  @groupby(uxl_user_follows){
                                a as count(uid)
                                }
                            var(func: type(UserExamLogs))@filter(eq(uxl_is_attempted,true) and eq(uxl_is_correct,false))  @groupby(uxl_user_follows){
                                b as count(uid)
                                }
                            var(func: type(UserExamLogs))@filter(eq(uxl_is_attempted,false)) @groupby(uxl_user_follows){
                                c as count(uid)
                                }
                            data(func: uid(a), orderdesc: val(a)) {
                                uid
                                email
                                fullname
                                total_correct : val(a)
                                total_incorrect : val(b)
                                total_skipped : val(c)                                
                                   }}

IT’s take 4 sec