Remove creations in gitlab_subscription_histories

In gitlab_subscription_histories table we don't track
gitlab_subscription creations anymore. This MR removes the existing
redundant rows in the gitlab.com database

db/post_migrate/20200113151354_remove_creations_in_gitlab_subscription_histories.rb

+# frozen_string_literal: true
+
+class RemoveCreationsInGitlabSubscriptionHistories < ActiveRecord::Migration[5.2]
+  DOWNTIME = false
+  GITLAB_SUBSCRIPTION_CREATED = 0
+
+  def up
+    return unless Gitlab.com?
+
+    delete_sql = "DELETE FROM gitlab_subscription_histories WHERE change_type=#{GITLAB_SUBSCRIPTION_CREATED} RETURNING *"
+
+    records = execute(delete_sql)
+
+    logger = Gitlab::BackgroundMigration::Logger.build
+    records.to_a.each do |record|
+      logger.info record.as_json.merge(message: "gitlab_subscription_histories with change_type=0 was deleted")
+    end
+  end
+
+  def down
+    # There's no way to restore, and the data is useless
+    # all the data to be deleted in case needed https://gitlab.com/gitlab-org/gitlab/uploads/7409379b0ed658624f5d33202b5668a1/gitlab_subscription_histories_change_type_0.sql.txt
+  end
+end

ee/changelogs/unreleased/118432-remove-creations-in-gitlab_subscription_histories.yml

+---
+title: Remove "creations" in gitlab_subscription_histories on gitlab.com
+merge_request: 22278
+author:
+type: other

ee/spec/migrations/remove_creations_in_gitlab_subscription_histories_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+require Rails.root.join('db', 'post_migrate', '20200113151354_remove_creations_in_gitlab_subscription_histories.rb')
+
+describe RemoveCreationsInGitlabSubscriptionHistories, :migration do
+  GITLAB_SUBSCRIPTION_CREATED = 0
+  GITLAB_SUBSCRIPTION_UPDATED = 1
+  GITLAB_SUBSCRIPTION_DESTROYED = 2
+
+  let(:gitlab_subscriptions) { table(:gitlab_subscriptions) }
+  let(:gitlab_subscription_histories) { table(:gitlab_subscription_histories) }
+
+  it 'removes creations in gitlab_subscription_histories on gitlab.com' do
+    allow(Gitlab).to receive(:com?).and_return(true)
+
+    gitlab_subscription = gitlab_subscriptions.create!
+    gitlab_subscription_histories.create! change_type: GITLAB_SUBSCRIPTION_CREATED,
+                                          gitlab_subscription_id: gitlab_subscription.id
+    gitlab_subscription_histories.create! change_type: GITLAB_SUBSCRIPTION_UPDATED,
+                                          seats: 13,
+                                          gitlab_subscription_id: gitlab_subscription.id
+    gitlab_subscription_histories.create! change_type: GITLAB_SUBSCRIPTION_DESTROYED,
+                                          seats: 13,
+                                          gitlab_subscription_id: gitlab_subscription.id
+
+    expect { migrate! }.to change { gitlab_subscription_histories.count }.from(3).to(2)
+    expect(gitlab_subscription_histories.where(change_type: [GITLAB_SUBSCRIPTION_UPDATED,
+                                                             GITLAB_SUBSCRIPTION_DESTROYED]).count) .to eq(2)
+    expect(gitlab_subscription_histories.where(change_type: GITLAB_SUBSCRIPTION_CREATED).count) .to eq(0)
+  end
+
+  it 'does not run if not on gitlab.com' do
+    allow(Gitlab).to receive(:com?).and_return(false)
+
+    gitlab_subscription = gitlab_subscriptions.create!
+    gitlab_subscription_histories.create! change_type: GITLAB_SUBSCRIPTION_CREATED,
+                                          gitlab_subscription_id: gitlab_subscription.id
+
+    expect { migrate! }.not_to change { gitlab_subscription_histories.count }
+    expect(gitlab_subscription_histories.count) .to eq(1)
+  end
+end