notifications/statistics returns when no stats exist for today

moved filtering from WHERE to JOIN ON so that when join suceeds but filter fails, we dont lose the service's data from the results set

tests/app/notifications/rest/test_notification_statistics.py

@@ -194,3 +194,32 @@ def test_get_notification_statistics_returns_both_existing_stats_and_generated_z
             assert generated_stats['service'] == str(service_without_stats.id)
 
             assert response.status_code == 200
+
+
+@freeze_time('1955-11-05T12:00:00')
+def test_get_notification_statistics_returns_zeros_when_only_stats_for_different_date(
+    notify_api,
+    sample_notification_statistics
+):
+    with notify_api.test_request_context():
+        with notify_api.test_client() as client:
+            with freeze_time('1985-10-26T00:06:00'):
+                auth_header = create_authorization_header(
+                    service_id=sample_notification_statistics.service_id
+                )
+                response = client.get(
+                    '/notifications/statistics?day={}'.format(date.today().isoformat()),
+                    headers=[auth_header]
+                )
+
+            notifications = json.loads(response.get_data(as_text=True))
+
+            assert response.status_code == 200
+            assert len(notifications['data']) == 1
+            assert notifications['data'][0]['emails_requested'] == 0
+            assert notifications['data'][0]['emails_delivered'] == 0
+            assert notifications['data'][0]['emails_failed'] == 0
+            assert notifications['data'][0]['sms_requested'] == 0
+            assert notifications['data'][0]['sms_delivered'] == 0
+            assert notifications['data'][0]['sms_failed'] == 0
+            assert notifications['data'][0]['service'] == str(sample_notification_statistics.service_id)