Wrong output in MYSQL -

i have question follows:

the total score of hacker sum of maximum scores of challenges. write query print hacker_id, name, , total score of hackers ordered descending score.
if more 1 hacker achieved same total score, sort result ascending hacker_id.
exclude hackers total score of 0 result.
2 tables given follows:

table: hackers

======================================== hacker_id: integer (id of hacker) name: string (name of hacker) ======================================== 

table: submissions

=================================================== submission_id: integer (id of submission) hacker_id:     integer (id of hacker) challenge_id:  integer (id of challenge) score:         integer (score of submission) =================================================== 

the mysql query i've written follows:-

select      a.hacker_id,     a.name,     a.total  from(     select          h.hacker_id,         h.name,         sum(case when s.hacker_id=h.hacker_id s.score else 0 end) total               hackers h,         submissions s      group          h.hacker_id,         h.name )       a.total>0  order      a.total desc,     a.hacker_id asc;  

i'm getting wrong output though output satisfies rules of order & ommission of 0 scorers required. i'm confused error is. please help!!!

the total score of hacker sum of maximum scores of challenges.

first, need find maximum score hacker, each challenge:

select hacker_id      , challenge_id      , max(score) max_score   submissions  group hacker_id         , challenge_id 

then need sum each hacker:

select hacker_id      , sum(max_score) total_score   ( select hacker_id               , challenge_id               , max(score) max_score            submissions           group hacker_id                  , challenge_id        ) ms  group hacker_id 

finally apply rest:

exclude hackers total score of 0 result.

print hacker_id, name, , total score

ordered descending score, ascending hacker_id.

select hacker_id      , ( select name            hackers h           h.hacker_id = ms.hacker_id        ) name      , sum(max_score) total_score   ( select hacker_id               , challenge_id               , max(score) max_score            submissions           group hacker_id                  , challenge_id        ) ms  group hacker_id having sum(max_score) <> 0  order total_score desc         , hacker_id