See blog post https://www.peterbe.com/plog/conditional-aggregation-in-django-2.0

indexable?.sql

explain analyze SELECT
  COUNT("upload_upload"."id") FILTER (WHERE ("upload_upload"."created_at" >= '2018-01-12T00:00:00.081739+00:00'::timestamptz AND "upload_upload"."created_at" < '2018-01-12T20:08:11.081739+00:00'::timestamptz)) AS "today_count",
  SUM("upload_upload"."size") FILTER (WHERE ("upload_upload"."created_at" >= '2018-01-12T00:00:00.081739+00:00'::timestamptz AND "upload_upload"."created_at" < '2018-01-12T20:08:11.081739+00:00'::timestamptz)) AS "today_total_size"
FROM "upload_upload";


explain analyze SELECT COUNT("upload_upload"."id") AS "count", SUM("upload_upload"."size") AS "total_size" FROM "upload_upload" WHERE ("upload_upload"."created_at" >= '2018-01-12T00:00:00.481487+00:00'::timestamptz AND "upload_upload"."created_at" < '2018-01-12T19:24:31.481487+00:00'::timestamptz);

output

                                                    QUERY PLAN
-------------------------------------------------------------------------------------------------------------------
 Aggregate  (cost=74.33..74.34 rows=1 width=16) (actual time=0.587..0.587 rows=1 loops=1)
   ->  Seq Scan on upload_upload  (cost=0.00..62.13 rows=813 width=16) (actual time=0.012..0.210 rows=813 loops=1)
 Planning time: 0.427 ms
 Execution time: 0.674 ms
(4 rows)

                                                                                  QUERY PLAN
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
 Aggregate  (cost=11.26..11.27 rows=1 width=8) (actual time=0.012..0.012 rows=1 loops=1)
   ->  Index Scan using upload_upload_created_at_8a54a254 on upload_upload  (cost=0.28..11.22 rows=8 width=8) (actual time=0.005..0.009 rows=16 loops=1)
         Index Cond: ((created_at >= '2018-01-11 19:00:00.481487-05'::timestamp with time zone) AND (created_at < '2018-01-12 14:24:31.481487-05'::timestamp with time zone))
 Planning time: 0.227 ms
 Execution time: 0.034 ms
(5 rows)