在 PostgreSql 8.4 查询中
explain analyze SELECT
max( kuupaev||kellaaeg ) as res
from ALGSA
where laonr=1 and kuupaev <='9999-12-31' and
kuupaev||kellaaeg <= '9999-12-3123 59'
运行需要 3 秒:
"Aggregate (cost=3164.49..3164.50 rows=1 width=10) (actual time=2714.269..2714.270 rows=1 loops=1)"
" -> Seq Scan on algsa (cost=0.00..3110.04 rows=21778 width=10) (actual time=0.105..1418.743 rows=70708 loops=1)"
" Filter: ((kuupaev <= '9999-12-31'::date) AND (laonr = 1::numeric) AND ((kuupaev || (kellaaeg)::text) <= '9999-12-3123 59'::text))"
"Total runtime: 2714.363 ms"
如何在 PostgreSQL 8.4.4 中加快速度?表结构如下。algsa 表在 kuupaev 上有索引也许可以使用?或者是否可以更改查询以添加一些其他索引以使其快速。表中的现有列无法更改。
CREATE TABLE firma1.algsa
(
id serial NOT NULL,
laonr numeric(2,0),
kuupaev date NOT NULL,
kellaaeg character(5) NOT NULL DEFAULT ''::bpchar,
... other columns
CONSTRAINT algsa_pkey PRIMARY KEY (id),
CONSTRAINT algsa_id_check CHECK (id > 0)
)
);
CREATE INDEX algsa_kuupaev_idx ON firma1.algsa USING btree (kuupaev);
更新
试过了analyze verbose firma1.algsa;
INFO: analyzing "firma1.algsa"
INFO: "algsa": scanned 1640 of 1640 pages, containing 70708 live rows and 13 dead rows; 30000 rows in sample, 70708 estimated total rows
Query returned successfully with no result in 1185 ms.
但查询运行时间仍然是 2.7 秒。
为什么有30000 rows in sample
。是不是太多了,应该减少吗?