Hello
2011/3/20 Adam Tistler <atist...@gmail.com>:
> I have noticed that SELECT ... = ANY(ARRAY(...)) is about twice as fast as
> SELECT IN ( ... ).
> Can anyone explain a reason for this? Results are the bottom and are
> reproducible. I can test with other versions if that is necessary.
>
send a result of EXPLAIN ANALYZE SELECT ..., please
The reasons can be different - less seq scans, indexes
Regards
Pavel Stehule
> ./configure --prefix=/usr/local/pgsql84 --with-openssl --with-perl
> CentOS release 5.4 (Final)
> psql (PostgreSQL) 8.4.1
>
> prompt2=# select count(*) from nodes;
> count
> --------
> 754734
> (1 row)
>
>
> prompt2=# \d nodes
> Table "public.nodes"
> Column | Type | Modifiers
> --------------+--------------------------+-----------------------------------------------------------
> node_id | integer | not null default
> nextval(('node_id_seq'::text)::regclass)
> node_type_id | integer | not null
> template_id | integer | not null
> timestamp | timestamp with time zone | default
> ('now'::text)::timestamp(6) with time zone
> Indexes:
> "nodes_pkey" PRIMARY KEY, btree (node_id)
> "n_node_id_index" btree (node_id)
> "n_node_type_id_index" btree (node_type_id)
> "n_template_id_index" btree (template_id)
>
> prompt2=# select count(*) from nodes where node_id = any( Array(select
> node_id from nodes limit 100000) );
> count
> --------
> 100000
> (1 row)
>
> Time: 404.530 ms
> prompt2=# select count(*) from nodes where node_id = any( Array(select
> node_id from nodes limit 100000) );
> count
> --------
> 100000
> (1 row)
>
> Time: 407.316 ms
> prompt2=# select count(*) from nodes where node_id = any( Array(select
> node_id from nodes limit 100000) );
> count
> --------
> 100000
> (1 row)
>
> Time: 408.728 ms
> prompt2=# select count(*) from nodes where node_id in (select node_id from
> nodes limit 100000 );
> count
> --------
> 100000
> (1 row)
>
> Time: 793.840 ms
> prompt2=# select count(*) from nodes where node_id in (select node_id from
> nodes limit 100000 );
> count
> --------
> 100000
> (1 row)
>
> Time: 779.137 ms
> prompt2=# select count(*) from nodes where node_id in (select node_id from
> nodes limit 100000 );
> count
> --------
> 100000
> (1 row)
>
> Time: 781.820 ms
>
>
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