Re: [SQL] Optimizing perfomance using indexes

Hello,

What version of PostgreSQL you're talking about ?
I also noticed such behaivour in 6.4 beta, try
int4 instead of int2 and see what happens. I don't know the reason
but in my case it works. 6.3.2 uses indices in both cases !

    Regards,
            Oleg

On Thu, 15 Oct 1998, Vladimir Litovka wrote:

> Date: Thu, 15 Oct 1998 15:35:53 +0300 (EEST)
> From: Vladimir Litovka <pgsqll@barnet.kharkov.ua>
> Reply-To: doka@root.webest.com
> To: PgSQL-sql <pgsql-sql@postgreSQL.org>
> Subject: [SQL] Optimizing perfomance using indexes
>
> Hello!
>
>  There are examples below and can anybody explain me - how to use indexes
>  in PostgreSQL for best perfomance? Look here:
>
>  create table aaa (num int2, name text);
>  create index ax on aaa (num);
>
>  explain select * from aaa where num = 5;
>          Index Scan on aaa  (cost=0.00 size=0 width=14)
>
>  explain select * from aaa where num > 5;
>          Seq Scan on aaa  (cost=0.00 size=0 width=14)
>
>  Why PostgreSQL in the first case uses index, but in the second - doesn't ?
>  As I understand, there is no big difference between queries. Are there
>  general recommendations on creating indexes?
>
>  This questions because I'm relatively new to SQL and hope somebody can
>  help me :) Thank you.
>
> ---
> Vladimir Litovka <doka@webest.com>
>
>

_____________________________________________________________
Oleg Bartunov, sci.researcher, hostmaster of AstroNet,
Sternberg Astronomical Institute, Moscow University (Russia)
Internet: oleg@sai.msu.su, http://www.sai.msu.su/~megera/
phone: +007(095)939-16-83, +007(095)939-23-83