Use EXTRACT(EPOCH) when calculating durations

ee/lib/gitlab/analytics/cycle_analytics/aggregated/data_for_duration_chart.rb

@@ -17,7 +17,7 @@ module Gitlab
           def average_by_day
             @query
               .group(date_expression)
-              .select(date_expression.as('date'), duration.average.as('average_duration_in_seconds'))
+              .select(date_expression.as('date'), duration_in_seconds.average.as('average_duration_in_seconds'))
           end
           # rubocop: enable CodeReuse/ActiveRecord
 

lib/gitlab/analytics/cycle_analytics/aggregated/median.rb

@@ -15,7 +15,7 @@ module Gitlab
 
           # rubocop: disable CodeReuse/ActiveRecord
           def seconds
-            @query = @query.select(median_duration_in_seconds.as('median')).reorder(nil)
+            @query = @query.select(duration_in_seconds(percentile_cont).as('median')).reorder(nil)
             result = @query.take || {}
 
             result['median'] || nil

lib/gitlab/analytics/cycle_analytics/aggregated/records_fetcher.rb

@@ -36,7 +36,7 @@ module Gitlab
 
           def serialized_records
             strong_memoize(:serialized_records) do
-              records = ordered_and_limited_query.select(stage_event_model.arel_table[Arel.star], duration.as('total_time'))
+              records = ordered_and_limited_query.select(stage_event_model.arel_table[Arel.star], duration_in_seconds.as('total_time'))
 
               yield records if block_given?
               issuables_and_records = load_issuables(records)

lib/gitlab/analytics/cycle_analytics/aggregated/stage_query_helpers.rb

@@ -27,13 +27,13 @@ module Gitlab
             end
           end
 
-          def median_duration_in_seconds
-            Arel::Nodes::Extract.new(percentile_cont, :epoch)
-          end
-
           def in_progress?
             params[:end_event_filter] == :in_progress
           end
+
+          def duration_in_seconds(duration_expression = duration)
+            Arel::Nodes::Extract.new(duration_expression, :epoch)
+          end
         end
       end
     end

spec/lib/gitlab/analytics/cycle_analytics/aggregated/records_fetcher_spec.rb

@@ -41,6 +41,19 @@ RSpec.describe Gitlab::Analytics::CycleAnalytics::Aggregated::RecordsFetcher do
         it_behaves_like 'match returned records'
       end
 
+      context 'when intervalstyle setting is configured to "postgres"' do
+        it 'avoids nil durations' do
+          # ActiveRecord cannot parse the 'postgres' intervalstyle, it returns nil
+          # The setting is rolled back after the test case.
+          Analytics::CycleAnalytics::IssueStageEvent.connection.execute("SET LOCAL intervalstyle='postgres'")
+
+          records_fetcher.serialized_records do |relation|
+            durations = relation.map(&:total_time)
+            expect(durations).to all(be > 0)
+          end
+        end
+      end
+
       context 'when sorting by end event ASC' do
         let(:expected_issue_ids) { [issue_2.iid, issue_1.iid, issue_3.iid] }