There is no need to have a separate table to store template monthly statistics. It's easy enough to aggregate the stats from ft_notification_status.

This removes the nightly task, and all the dao methods.
The next PR will remove the table.

tests/app/celery/test_scheduled_tasks.py

@@ -1,4 +1,3 @@
-import functools
 from datetime import datetime, timedelta
 from functools import partial
 from unittest.mock import call, patch, PropertyMock
@@ -31,7 +30,6 @@ from app.celery.scheduled_tasks import (
     send_total_sent_notifications_to_performance_platform,
     switch_current_sms_provider_on_slow_delivery,
     timeout_notifications,
-    daily_stats_template_usage_by_month,
     letter_raise_alert_if_no_ack_file_for_zip,
     replay_created_notifications
 )
@@ -46,8 +44,6 @@ from app.dao.provider_details_dao import (
 )
 from app.exceptions import NotificationTechnicalFailureException
 from app.models import (
-    NotificationHistory,
-    StatsTemplateUsageByMonth,
     JOB_STATUS_IN_PROGRESS,
     JOB_STATUS_ERROR,
     LETTER_TYPE,
@@ -69,7 +65,6 @@ from tests.app.db import (
 from tests.app.conftest import (
     sample_job as create_sample_job,
     sample_notification_history as create_notification_history,
-    sample_template as create_sample_template,
     datetime_in_past
 )
 
@@ -806,151 +801,6 @@ def test_check_job_status_task_sets_jobs_to_error(mocker, sample_template):
     assert job_2.job_status == JOB_STATUS_IN_PROGRESS
 
 
-def test_daily_stats_template_usage_by_month(notify_db, notify_db_session):
-    notification_history = functools.partial(
-        create_notification_history,
-        notify_db,
-        notify_db_session,
-        status='delivered'
-    )
-
-    template_one = create_sample_template(notify_db, notify_db_session)
-    template_two = create_sample_template(notify_db, notify_db_session)
-
-    notification_history(created_at=datetime(2017, 10, 1), sample_template=template_one)
-    notification_history(created_at=datetime(2016, 4, 1), sample_template=template_two)
-    notification_history(created_at=datetime(2016, 4, 1), sample_template=template_two)
-    notification_history(created_at=datetime.now(), sample_template=template_two)
-
-    daily_stats_template_usage_by_month()
-
-    result = db.session.query(
-        StatsTemplateUsageByMonth
-    ).order_by(
-        StatsTemplateUsageByMonth.year,
-        StatsTemplateUsageByMonth.month
-    ).all()
-
-    assert len(result) == 2
-
-    assert result[0].template_id == template_two.id
-    assert result[0].month == 4
-    assert result[0].year == 2016
-    assert result[0].count == 2
-
-    assert result[1].template_id == template_one.id
-    assert result[1].month == 10
-    assert result[1].year == 2017
-    assert result[1].count == 1
-
-
-def test_daily_stats_template_usage_by_month_no_data():
-    daily_stats_template_usage_by_month()
-
-    results = db.session.query(StatsTemplateUsageByMonth).all()
-
-    assert len(results) == 0
-
-
-def test_daily_stats_template_usage_by_month_multiple_runs(notify_db, notify_db_session):
-    notification_history = functools.partial(
-        create_notification_history,
-        notify_db,
-        notify_db_session,
-        status='delivered'
-    )
-
-    template_one = create_sample_template(notify_db, notify_db_session)
-    template_two = create_sample_template(notify_db, notify_db_session)
-
-    notification_history(created_at=datetime(2017, 11, 1), sample_template=template_one)
-    notification_history(created_at=datetime(2016, 4, 1), sample_template=template_two)
-    notification_history(created_at=datetime(2016, 4, 1), sample_template=template_two)
-    notification_history(created_at=datetime.now(), sample_template=template_two)
-
-    daily_stats_template_usage_by_month()
-
-    template_three = create_sample_template(notify_db, notify_db_session)
-
-    notification_history(created_at=datetime(2017, 10, 1), sample_template=template_three)
-    notification_history(created_at=datetime(2017, 9, 1), sample_template=template_three)
-    notification_history(created_at=datetime(2016, 4, 1), sample_template=template_two)
-    notification_history(created_at=datetime(2016, 4, 1), sample_template=template_two)
-    notification_history(created_at=datetime.now(), sample_template=template_two)
-
-    daily_stats_template_usage_by_month()
-
-    result = db.session.query(
-        StatsTemplateUsageByMonth
-    ).order_by(
-        StatsTemplateUsageByMonth.year,
-        StatsTemplateUsageByMonth.month
-    ).all()
-
-    assert len(result) == 4
-
-    assert result[0].template_id == template_two.id
-    assert result[0].month == 4
-    assert result[0].year == 2016
-    assert result[0].count == 4
-
-    assert result[1].template_id == template_three.id
-    assert result[1].month == 9
-    assert result[1].year == 2017
-    assert result[1].count == 1
-
-    assert result[2].template_id == template_three.id
-    assert result[2].month == 10
-    assert result[2].year == 2017
-    assert result[2].count == 1
-
-    assert result[3].template_id == template_one.id
-    assert result[3].month == 11
-    assert result[3].year == 2017
-    assert result[3].count == 1
-
-
-def test_dao_fetch_monthly_historical_stats_by_template_null_template_id_not_counted(notify_db, notify_db_session):
-    notification_history = functools.partial(
-        create_notification_history,
-        notify_db,
-        notify_db_session,
-        status='delivered'
-    )
-
-    template_one = create_sample_template(notify_db, notify_db_session, template_name='1')
-    history = notification_history(created_at=datetime(2017, 2, 1), sample_template=template_one)
-
-    NotificationHistory.query.filter(
-        NotificationHistory.id == history.id
-    ).update(
-        {
-            'template_id': None
-        }
-    )
-
-    daily_stats_template_usage_by_month()
-
-    result = db.session.query(
-        StatsTemplateUsageByMonth
-    ).all()
-
-    assert len(result) == 0
-
-    notification_history(created_at=datetime(2017, 2, 1), sample_template=template_one)
-
-    daily_stats_template_usage_by_month()
-
-    result = db.session.query(
-        StatsTemplateUsageByMonth
-    ).order_by(
-        StatsTemplateUsageByMonth.year,
-        StatsTemplateUsageByMonth.month
-    ).all()
-
-    assert len(result) == 1
-
-
 def mock_s3_get_list_match(bucket_name, subfolder='', suffix='', last_modified=None):
     if subfolder == '2018-01-11/zips_sent':
         return ['NOTIFY.20180111175007.ZIP.TXT', 'NOTIFY.20180111175008.ZIP.TXT']