Updates after review

- Modified the services_dao to return an int instead of a datetime to
make usage easier and removed the BST function on year as it is not
relevant for year
- Improved tests do there is less logic by ordering the result so there
is less reliance on the template id
- Renamed variable in stats_template_usage_by_month_dao.py to make it
consistent with the method

app/dao/services_dao.py

@@ -40,7 +40,7 @@ from app.models import (
 )
 from app.service.statistics import format_monthly_template_notification_stats
 from app.statsd_decorators import statsd
-from app.utils import get_london_month_from_utc_column, get_london_midnight_in_utc, get_london_year_from_utc_column
+from app.utils import get_london_month_from_utc_column, get_london_midnight_in_utc
 from app.dao.annual_billing_dao import dao_insert_annual_billing
 
 DEFAULT_SERVICE_PERMISSIONS = [
@@ -525,13 +525,13 @@ def dao_fetch_active_users_for_service(service_id):
 @statsd(namespace="dao")
 def dao_fetch_monthly_historical_stats_by_template():
     month = get_london_month_from_utc_column(NotificationHistory.created_at)
-    year = get_london_year_from_utc_column(NotificationHistory.created_at)
+    year = func.date_trunc("year", NotificationHistory.created_at)
     end_date = datetime.combine(date.today(), time.min)
 
     return db.session.query(
         NotificationHistory.template_id,
-        month.label('month'),
-        year.label('year'),
+        extract('month', month).label('month'),
+        extract('year', year).label('year'),
         func.count().label('count')
     ).filter(
         NotificationHistory.created_at < end_date