Looking for the best way to request sql stats over years for each sellers from my db

my_stats.rb

@top_sellers = Turnover.
                 joins(:seller).
                 select('SUM(turnovers.amount) AS total_current_year, SUM(turnovers.amount) AS total_last_year, sellers.*').
                 where('turnovers.year = ?', 2013).
                 group('turnovers.seller_id').
                 order('total_current_year DESC').
                 limit(5)
    
@worst_sellers = Turnover.
                   joins(:seller).
                   select('SUM(turnovers.amount) AS total_current_year, SUM(turnovers.amount) AS total_last_year, sellers.*').
                   where('turnovers.year = ?', 2013).
                   group('turnovers.seller_id').
                   order('total_current_year ASC').
                   limit(5)

@turnovers = Turnover.select('turnovers.*, SUM(turnovers.amount) AS total').group(:year).order('year DESC')
result = Turnover.find_by_sql('SELECT SUM(CASE WHEN turnovers.year = 2013 THEN turnovers.amount END) AS total_current_year, SUM(CASE WHEN turnovers.year = 2012 THEN turnovers.amount END) AS total_last_year, sellers.* FROM `turnovers` INNER JOIN `sellers` ON `sellers`.`id` = `turnovers`.`seller_id` GROUP BY turnovers.seller_id ORDER BY total_current_year DESC')

@top_sellers = result[0..4]
@worst_sellers = result.reverse[0..4]