Question

我已经阅读了很多关于日期索引的文章，但我无法在时间戳上正确使用索引。

我的表：

CREATE TABLE registration
(
  id_reg serial NOT NULL,
  pass_uid character varying(12) NOT NULL,
  direction smallint NOT NULL,
  country character varying(255) NOT NULL,
  fly_number character varying(10) NOT NULL,
  the_date timestamp without time zone NOT NULL DEFAULT now(),
  user_id integer NOT NULL,
  station_number integer NOT NULL,
  fir bytea,
  CONSTRAINT registration_pkey PRIMARY KEY (id_reg)
)

我在the_date列上创建了索引：

CREATE INDEX ON registration ((the_date::timestamp));

但我的查询并未使用索引：

 explain select * from registration where the_date between '2001-01-01 00:00:00' and '2015-12-31 00:00:00';

"Seq Scan on registration  (cost=0.00..49481.00 rows=932106 width=232)  (actual time=0.401..1028.491 rows=932466 loops=1)"
"  Filter: ((the_date >= '2001-01-01 00:00:00'::timestamp without time zone) AND (the_date <= '2015-12-31 00:00:00'::timestamp without time zone))"
"  Rows Removed by Filter: 67534"
"Planning time: 0.538 ms"
"Execution time: 1078.553 ms"

然后我删除了旧索引并创建了新索引：

CREATE INDEX ON registration ((the_date::date));

explain analyze select * from registration where the_date between '2001-01-01' and '2015-12-31';

"Seq Scan on registration  (cost=0.00..49481.00 rows=932010 width=232) (actual time=0.016..738.757 rows=932466 loops=1)"
"  Filter: ((the_date >= '2001-01-01 00:00:00'::timestamp without time zone) AND (the_date <= '2015-12-31 00:00:00'::timestamp without time zone))"
"  Rows Removed by Filter: 67534"
"Planning time: 0.207 ms"
"Execution time: 786.233 ms"

我使用的是配备英特尔赛扬2.16 GHz双核，内存为2 GB的PC和Postgres配置：

 shared_buffers=256MB
 effective_cache_size=1GB,
 work_mem=64MB
 synchronize_commit=off.

你能帮我解决这个问题。提前致谢

为什么没有关于timestamp列的索引

0 个答案: