diff --git a/app/helpers/statistics_helper.rb b/app/helpers/statistics_helper.rb
index a43bc94c..391e7e98 100644
--- a/app/helpers/statistics_helper.rb
+++ b/app/helpers/statistics_helper.rb
@@ -71,15 +71,14 @@ module StatisticsHelper
       {
         key: 'submissions_per_minute',
           name: t('statistics.entries.exercises.submissions_per_minute'),
-          data: (Submission.where('created_at >= ?', DateTime.now - 1.hour).count.to_f / 60).round(2),
+          data: (Submission.where(created_at: DateTime.now - 1.hour..).count.to_f / 60).round(2),
           unit: '/min',
           url: statistics_graphs_path,
       },
       {
         key: 'autosaves_per_minute',
           name: t('statistics.entries.exercises.autosaves_per_minute'),
-          data: (Submission.where('created_at >= ?',
-            DateTime.now - 1.hour).where(cause: 'autosave').count.to_f / 60).round(2),
+          data: (Submission.where(created_at: DateTime.now - 1.hour..).where(cause: 'autosave').count.to_f / 60).round(2),
           unit: '/min',
       },
       {
@@ -121,13 +120,13 @@ module StatisticsHelper
         key: 'active_in_last_hour',
           name: t('statistics.entries.users.currently_active'),
           data: ExternalUser.joins(:submissions)
-            .where(['submissions.created_at >= ?', DateTime.now - 5.minutes])
+            .where(submissions: {created_at: DateTime.now - 5.minutes..})
             .distinct('external_users.id').count,
       },
       {
         key: 'submissions_per_minute',
           name: t('statistics.entries.exercises.submissions_per_minute'),
-          data: (Submission.where('created_at >= ?', DateTime.now - 1.hour).count.to_f / 60).round(2),
+          data: (Submission.where(created_at: DateTime.now - 1.hour..).count.to_f / 60).round(2),
           unit: '/min',
           axis: 'right',
       },
diff --git a/app/models/request_for_comment.rb b/app/models/request_for_comment.rb
index 8f6d5503..38ca4c0d 100644
--- a/app/models/request_for_comment.rb
+++ b/app/models/request_for_comment.rb
@@ -85,7 +85,7 @@ class RequestForComment < ApplicationRecord
 
     def last_per_user(count = 5)
       from(row_number_user_sql, :request_for_comments)
-        .where('row_number <= ?', count)
+        .where(row_number: ..count)
         .group('request_for_comments.id, request_for_comments.user_id, request_for_comments.user_type, ' \
                'request_for_comments.exercise_id, request_for_comments.file_id, request_for_comments.question, ' \
                'request_for_comments.created_at, request_for_comments.updated_at, request_for_comments.solved, ' \
diff --git a/db/migrate/20201019090123_add_normalized_score_and_submission_to_user_exercise_feedback.rb b/db/migrate/20201019090123_add_normalized_score_and_submission_to_user_exercise_feedback.rb
index 2fc9e8ff..04a55e3c 100644
--- a/db/migrate/20201019090123_add_normalized_score_and_submission_to_user_exercise_feedback.rb
+++ b/db/migrate/20201019090123_add_normalized_score_and_submission_to_user_exercise_feedback.rb
@@ -10,7 +10,7 @@ class AddNormalizedScoreAndSubmissionToUserExerciseFeedback < ActiveRecord::Migr
     UserExerciseFeedback.find_each do |uef|
       latest_submission = Submission
         .where(user_id: uef.user_id, user_type: uef.user_type, exercise_id: uef.exercise_id)
-        .where('created_at < ?', uef.updated_at)
+        .where(created_at: ...uef.updated_at)
         .order(created_at: :desc).first
 
       # In the beginning, CodeOcean allowed feedback for exercises while viewing an RfC. As a RfC