From: Franco Bruno Borghesi <franco@akyasociados.com.ar>
To: Phil Endecott <spam_from_postgresql_sql@chezphil.org>
Cc: pgsql-sql@postgresql.org
Subject: Re: Need indexes on inherited tables?
Date: Sat, 26 Jun 2004 18:06:20 -0300
Message-ID: <1088283980.1215.19.camel@taz.oficina> (raw)
In-Reply-To: <1902614@chezphil.org>
References: <1902614@chezphil.org>
Table T is not inheriting any indexes, neither the primary key
constraint. That means that the search is going to use an index scan on
table B and a sequential scan on table T (unless of course you add a
primary key constraint or an index on table T).
You can check this things doing:
->SET enable_seqscan TO off;
->EXPLAIN SELECT * FROM B WHERE id=5;
you'll see an index scan on table B and sequential scans on the other
tables.
Doing:
->SELECT C.relname AS table_name, C2.relname AS index_name FROM pg_index
I LEFT JOIN pg_class C ON (I.indrelid=C.oid) LEFT JOIN pg_class C2 ON
(C2.oid=I.indexrelid) WHERE C.relname ILIKE '<table_name>'
you can find out what indexes are available for table_name (or \d
<table_name> in psql).
On Sat, 2004-06-26 at 16:29, Phil Endecott wrote:
> Dear Postgresql experts,
>
> I have a base table that declares a primary key spanning a couple of columns:
>
> create table B (
> id integer,
> xx someothertype,
> .....
> primary key (id, xx)
> );
>
> and a number of derived tables that inherit from B:
>
> create table T (
> ....
> ) inherits (B);
>
> An index is automatically created for B because of the primary key.
>
> If I search for something in T using the key columns, e.g. I do
>
> select * from T where id=1 and xx=something;
>
> will the index be used? Or must I explicity create an index on id and xx for T and each of the other derived tables?
>
> Is it any different if I search in B and find rows that are actually in T?
>
> (Slightly unrelated: does the index on (id,xx) help when I am searching only on id?)
>
> Thanks for any insight anyone can offer.
>
> --Phil.
>
> ---------------------------(end of broadcast)---------------------------
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>
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To: pgsql-sql@postgresql.org
Cc: franco@akyasociados.com.ar, spam_from_postgresql_sql@chezphil.org
Subject: Re: Need indexes on inherited tables?
In-Reply-To: <1088283980.1215.19.camel@taz.oficina>
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