Use postgres interval explicitly for all default occasions

app/models/exercise.rb

@@ -215,7 +215,9 @@ class Exercise < ApplicationRecord
                           "AND user_id = #{user.id} AND user_type = '#{user.class.name}'"
                         end
 
-    results = self.class.connection.execute(study_group_working_time_query(id, study_group_id, additional_filter)).each do |tuple|
+    results = ActiveRecord::Base.transaction do
+      self.class.connection.execute("SET LOCAL intervalstyle = 'postgres'")
+      self.class.connection.execute(study_group_working_time_query(id, study_group_id, additional_filter)).each do |tuple|
         bucket = if maximum_score > 0.0 && tuple['score'] <= maximum_score
                    (tuple['score'] / maximum_score * max_bucket).round
                  else
@@ -230,6 +232,7 @@ class Exercise < ApplicationRecord
         additional_user_data[bucket][tuple['index']] = {start_time: tuple['start_time'], score: tuple['score']}
         additional_user_data[max_bucket + 1][tuple['index']] = {id: tuple['user_id'], type: tuple['user_type'], name: tuple['name']}
       end
+    end
 
     if results.ntuples > 0
       first_index = results[0]['index']
@@ -366,18 +369,24 @@ class Exercise < ApplicationRecord
 
   def retrieve_working_time_statistics
     @working_time_statistics = {}
+    ActiveRecord::Base.transaction do
+      self.class.connection.execute("SET LOCAL intervalstyle = 'postgres'")
       self.class.connection.execute(user_working_time_query).each do |tuple|
         @working_time_statistics[tuple['user_id'].to_i] = tuple
       end
     end
+  end
 
   def average_working_time
+    ActiveRecord::Base.transaction do
+      self.class.connection.execute("SET LOCAL intervalstyle = 'postgres'")
       self.class.connection.execute(''"
       SELECT avg(working_time) as average_time
       FROM
         (#{user_working_time_query}) AS baz;
     "'').first['average_time']
     end
+  end
 
   def average_working_time_for(user_id)
     retrieve_working_time_statistics if @working_time_statistics.nil?
@@ -389,7 +398,6 @@ class Exercise < ApplicationRecord
     begin
       result = ActiveRecord::Base.transaction do
         self.class.connection.execute(''"
-              BEGIN;
               SET LOCAL intervalstyle = 'iso_8601';
               WITH WORKING_TIME AS
               (SELECT user_id,
@@ -531,7 +539,7 @@ class Exercise < ApplicationRecord
   end
 
   def finishers
-    ExternalUser.joins(:submissions).where(submissions: {exercise_id: id, score: maximum_score, cause: %w[submit assess]}).distinct
+    ExternalUser.joins(:submissions).where(submissions: {exercise_id: id, score: maximum_score, cause: %w[submit assess remoteSubmit remoteAssess]}).distinct
   end
 
   def set_default_values