Rails Average multiple columns - ruby-on-rails

Question

I need to find the average of multiple columns based on a params search across several tables in my VPC controller, but i'm having trouble displaying the average results in the view and also the search is very slow to read from the database. Wondering the best method to do below would be. Would it be best to do the averages in the model? (not sure how this is done though)
Models
class Vpc < ActiveRecord::Base
has_many :results
end
class Result < ActiveRecord::Base
attr_accessible :trial_id, :variety_id, :year, :lint, :turnout, :length_decimal, :length_imperial, :strength, :uniformity, :micronaire, :manual_class
belongs_to :trial, :primary_key => 'trial_id'
belongs_to :variety, :primary_key => 'variety_id'
belongs_to :vpc
has_many :sites, :through => :trial
has_many :growers, :through => :trial
has_many :regions, :through => :sites
end
Controller
class VpcController < ApplicationController
add_breadcrumb "Home", :root_url
add_breadcrumb "Variety Performance Comparison", :vpc_index_path
def index
all = Result.select(:variety_id)
#variety = Variety.where(:variety_id => all).order('variety_name DESC')
#years = Result.select('DISTINCT year')
#regions = Region.all
#irrigations = Trial.select('DISTINCT irrigated').order('irrigated ASC')
end
def search
if params[:variety_one] != params[:variety_two]
#comparison = Result.group('trials.trial_id').having('COUNT(*) = 2').where(variety_id: [params[:variety_one], params[:variety_two]]).
joins(:trial).where('trials.irrigated' => params[:irrigated], 'year' => params[:year]).joins(:regions).where('sites.region_id' => params[:regions])
#vone = #comparison.where('variety_id = ?', params[:variety_one]).select('avg(lint) AS lintone')
#vtwo = #comparison.where('variety_id = ?', params[:variety_two]).select('avg(lint) as linttwo')
#count = #comparison.count('DISTINCT results.trial_id')
#years = #comparison.where('results.year' => params[:year]).select('DISTINCT results.year')
#region = #comparison.where('sites.region_id' => params[:regions]).joins(:regions).group('regions.region_id').select("DISTINCT regions.name")
else
redirect_to vpc_index_url, notice: "Can't compare the same variety"
end
#variety_one = Variety.where('variety_id = ?', params[:variety_one]).group('variety_name')
#variety_two = Variety.where('variety_id = ?', params[:variety_two]).group('variety_name')
add_breadcrumb "Results"
end
end
View Results
<h2>VPC</h2>
<p>We found <%= #count.count %> trials that matched your options, spanning <%= #years.length %> years (<%= #years.map{|y| y.year}.join(", ") %>) and <%= #region.length %> regions (<%= #region.map{|r| r.trial.site.region.name}.join(", ") %>).</p>
<table class="table">
<th></th>
<% #variety_one.each do |v| %>
<th><%= v.variety_name %></th>
<% end %>
<% #variety_two.each do |v| %>
<th><%= v.variety_name %></th>
<% end %>
<th>Difference</th>
<tr>
<td>Yield (bales/ha)</td>
<td><%= "%.2f" % (#vone.lintone/227) unless #vone.blank? %></td>
<td><%= "%.2f" % (#vtwo.lintwo/227) unless #vtwo.blank? %></td>
<td><%= "%.2f" % ((#vone.lintone/227) - (#vtwo.lintwo/227)) unless #lintone.blank? %></td>
</tr>
</tr>
</table>
<hr>
<div class="accordion" id="accordion2">
<div class="accordion-group">
<div class="accordion-heading">
<a class="accordion-toggle" data-toggle="collapse" data-parent="#accordion2" href="#collapseOne">
<b>Overview of results</b> <span class="pull-right"><i class="icon-chevron-down"></i></span>
</a>
</div>
<div id="collapseOne" class="accordion-body collapse">
<div class="accordion-inner">
<table class="table">
<th>Year</th>
<th>Site</th>
<th>Region</th>
<th>Grower</th>
<% #comparison.each do |v| %>
<tr>
<td><%= link_to v.trial.year, trial_trials_path(trial_id: v.trial_id) %></td>
<td><%= link_to v.trial.site.site_name, trial_trials_path(trial_id: v.trial_id) unless v.trial.site.blank? %></td>
<td><%= link_to v.trial.site.region.name, trial_trials_path(trial_id: v.trial_id) unless v.trial.site.blank? %></td>
<td><%= link_to v.trial.grower.full_name, trial_trials_path(trial_id: v.trial_id) unless v.trial.grower.blank? %></td>
</tr>
<% end %>
</table>
</div>
</div>
</div>
SQL Error
Mysql2::Error: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'AS lintone) AS count_avg_lint_as_lintone, avg(lint) AS lintone, trials.trial_id ' at line 1: SELECT COUNT(avg(lint) AS lintone) AS count_avg_lint_as_lintone, avg(lint) AS lintone, trials.trial_id AS trials_trial_id FROM `results` INNER JOIN `trials` ON `trials`.`trial_id` = `results`.`trial_id` INNER JOIN `trials` `trials_results_join` ON `trials_results_join`.`trial_id` = `results`.`trial_id` INNER JOIN `sites` ON `sites`.`site_id` = `trials_results_join`.`site_id` INNER JOIN `regions` ON `regions`.`region_id` = `sites`.`region_id` WHERE `results`.`variety_id` IN (2300, 2255) AND `trials`.`irrigated` IN (0, 1, 2) AND `results`.`year` IN (2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013) AND `sites`.`region_id` IN (1, 2, 3, 4, 5, 6, 7, 8) AND (variety_id = '2300') GROUP BY trials.trial_id HAVING COUNT(*) = 2

Answer 1

Looking at your massive controller, I would suggest the following:
#comparison = Result.group('trials.trial_id').having('COUNT(*) = 2').where(variety_id: [params[:variety_one], params[:variety_two]]).
joins(:trial).where('trials.irrigated' => params[:irrigated], 'year' => params[:year]).joins(:regions).where('sites.region_id' => params[:regions])
#count = #comparison.count('DISTINCT results.trial_id')
#years = #comparison.where('results.year' => params[:year]).select('DISTINCT results.year')
#region = #comparison.where('sites.region_id' => params[:regions]).joins(:regions).group('regions.region_id').select("DISTINCT regions.name")
Keep that chunk the same but create a migration to add indexes to increase the performance.
You should not call average so many times but instead do a select on the values you want
#vone = #comparison.where('variety_id = ?', params[:variety_one]).select(avg(lint) as lint, avg...
#vtwo = #comparison.where('variety_id = ?', params[:variety_two]).select(avg(lint) as lint, avg...)
Now in your views you can just get the needed attributes.
After that, have a look at the logs to see if there are any N+1 you can reduce.