ruby on rails - Active Record or SQL query for leaderboard (postgres rank and sum) -

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i looking or creating advanced query in rails/active record (or sql using postgres) contest.

i have contest table, users table , activities table. contests have many users (participants) , users have many activities. each activity has points, 'trackable_type', , other attributes.

what want selected: - first_name users table - last_name users table - sum of points each user total_contest_points - count of activities have type 'course' each user total_contest_courses - results returned ranked total_contest_points , total_contest_courses

i have taken @ postgres_ext gem , tried writing sql, can't seem ranking work. here's have far:

time_range = start_time..end_time contestants = participants.joins(:activities).where('activities.created_at' => time_range).select("   users.id,   users.first_name,   users.last_name,   sum(activities.points) total_contest_points,   sum(     case     when       activities.trackable_type='course'           1     else       0     end   ) total_contest_courses,   rank() on (order total_contest_points desc) contest_rank ").group('users.id').limit(limit)

thanks , suggestions.


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