Group params in rails 3.2 - ruby-on-rails

Question

I have a search form with two drop down options with varieties (params[:variety_one], params[:variety_two]). Once submitted I want to display the results of both varieties if they only exist in the trial_id column. The variety_id column has multiple enteries per trial_id.
e.g
trial_id | variety_id
444 | 2300
444 | 2255
444 | 3450
445 | 2300
445 | 3450
446 | 2300
446 | 2255
446 | 5567
So if the user selected varieties 2300 and 2255 then it would only hit trial_id's 444 and 446 not 455 as variety 2300 only exists.
This is my controller so far.
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
#comparison = Result.group(:trial_id).where(variety_id: [params[:variety_one], params[:variety_two]]).having('COUNT(*) = 2').joins(:trial).where('trials.irrigated' => params[:irrigated], 'year' => params[:year]).joins(:regions).where('sites.region_id' => params[:regions])
end
This is the error I am getting
Mysql2::Error: Column 'trial_id' in field list is ambiguous: SELECT COUNT(DISTINCT results.trial_id) AS count_distinct_results_trial_id, trial_id AS 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, 2014) AND `sites`.`region_id` IN (1, 2, 3, 4, 5, 6, 7, 8) GROUP BY trial_id HAVING COUNT(*) = 2
If i remove the group(:trial_id) it works, but it grabs all the variety_id's selected.
Form
<% #options = ['Dryland', 'Irrigated', 'Semi-irrigated'] %>
<%= form_tag vpc_search_path do %>
<div class="row-fluid">
<div class="span2"></div>
<div class="span4" style="text-align: center; padding: 10px 0 10px 0;">
<h5 style="padding-bottom: 10px; text-align: center;">Select Variety One</h5>
<%= select_tag :variety_one, options_from_collection_for_select(#variety, "variety_id", "variety_name", :selected => "2300"), include_blank: false %>
</div>
<div class="span4" style="text-align: center; padding: 10px 0 10px 0;">
<h5 style="padding-bottom: 10px; text-align: center;">Select Variety Two</h5>
<%= select_tag :variety_two, options_from_collection_for_select(#variety, "variety_id", "variety_name", :selected => "2255"), include_blank: false %>
</div>
<div class="span2"></div>
</div>
<div class="row-fluid">
<div class="span12" style="text-align: center; padding: 10px 0 10px 0;">
<h5 style="padding-bottom: 10px; text-align: center;">Trial Type</h5>
<% #irrigations.each do |i| %>
<div class="checkbox inline"><%= check_box_tag 'irrigated[]', i.irrigated, true %>
<% if i.irrigated == 0 %> <%= #options[0] %> <% end %>
<% if i.irrigated == 1 %> <%= #options[1] %> <% end %>
<% if i.irrigated == 2 %> <%= #options[2] %> <% end %>
</div>
<% end %>
</div>
</div>
<div class="row-fluid">
<div class="span2"></div>
<div class="span4" style="text-align: center; padding: 10px 0 10px 0;">
<h5 style="padding-bottom: 10px; text-align: center;">Select Years</h5>
<% #years.each do |y| %>
<%= check_box_tag 'year[]', y.year, true %> <%= y.year %></br>
<% end %>
</div>
<div class="span4" style="padding: 10px 0 10px 85px;">
<h5 style="padding-bottom: 10px;">Select Regions</h5>
<% #regions.each do |r| %>
<%= check_box_tag 'regions[]', r.region_id, true %> <%= r.name %></br>
<% end %>
</div>
<div class="span2"></div>
</div>
<div class="row-fluid">
<div class="span12" style="text-align: center; padding-top: 10px;">
<%= submit_tag "Compare" %>
<% end %>
</div>
</div>

Answer 1

def index
results_ids = Result.pluck('variety_id') ## use pluck here
#variety = Variety.where(:variety_id => results_ids).order('variety_name DESC')
#years = Result.select('DISTINCT year') # do you really need an object here? pluck?
#regions = Region.all # ok, all, really? large table?
#irrigations = Trial.select('DISTINCT irrigated').order('irrigated ASC')
end
def search
#comparison = Result.group('results.trial_id')
.where(variety_id: [params[:variety_one], params[:variety_two]])
.having('COUNT(*) = 2').joins(:trial)
.where('trials.irrigated' => params[:irrigated], 'year' => params[:year])
.joins(:regions).where('sites.region_id' => params[:regions])
end
generally speaking, whenever you get column is ambiguous you got to attach table name with it in your request cause rails is not able to form the full request to database itself