在PostgreSQL中，我在tickets表的日期字段上有一个索引。当我将字段与进行比较时now()，查询效率很高：

# explain analyze select count(1) as count from tickets where updated_at > now();
                                                             QUERY PLAN                                                                  
---------------------------------------------------------------------------------------------------------------------------------------------
Aggregate  (cost=90.64..90.66 rows=1 width=0) (actual time=33.238..33.238 rows=1 loops=1)
   ->  Index Scan using tickets_updated_at_idx on tickets  (cost=0.01..90.27 rows=74 width=0) (actual time=0.016..29.318 rows=40250 loops=1)
         Index Cond: (updated_at > now())
Total runtime: 33.271 ms

如果我尝试将其与now()负间隔进行比较，它会下坡并使用位图堆扫描。

# explain analyze select count(1) as count from tickets where updated_at > (now() - '24 hours'::interval);
                                                                  QUERY PLAN
-----------------------------------------------------------------------------------------------------------------------------------------------------
Aggregate  (cost=180450.15..180450.17 rows=1 width=0) (actual time=543.898..543.898 rows=1 loops=1)
->  Bitmap Heap Scan on tickets  (cost=21296.43..175963.31 rows=897368 width=0) (actual time=251.700..457.916 rows=924373 loops=1)
     Recheck Cond: (updated_at > (now() - '24:00:00'::interval))
     ->  Bitmap Index Scan on tickets_updated_at_idx  (cost=0.00..20847.74 rows=897368 width=0)     (actual time=238.799..238.799 rows=924699 loops=1)
           Index Cond: (updated_at > (now() - '24:00:00'::interval))
Total runtime: 543.952 ms

有没有一种更有效的使用日期算术查询的方法？