From: K C Lau <kclau60@netvigator.com>
To: Jim C. Nasby <jnasby@pervasive.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: SELECT MIN, MAX took longer time than SELECT
Date: Sat, 21 Jan 2006 21:12:47 +0800
Message-ID: <6.2.1.2.0.20060121210512.08cc9310@localhost> (raw)
In-Reply-To: <20060120172026.GF20182@pervasive.com>
References: <6.2.1.2.0.20060120120150.08ab7b00@localhost>
<20060120172026.GF20182@pervasive.com>
At 01:20 06/01/21, Jim C. Nasby wrote:
>BTW, these queries below are meaningless; they are not equivalent to
>min(logsn).
>
> > esdt=> explain analyze select LogSN from Log where create_time <
> > '2005/10/19' order by create_time limit 1;
Thank you for pointing it out.
It actually returns the min(logsn), as the index is on (create_time,
logsn). To be more explicit, I have changed to query to:
explain analyze select LogSN from Log where create_time < '2005/10/19'
order by create_time, logsn limit 1;
esdt=> \d log;
create_time | character varying(23) | default
'1970/01/01~00:00:00.000'::character varying
logsn | integer | not null
...
Indexes:
"pk_log" PRIMARY KEY, btree (logsn)
"idx_logtime" btree (create_time, logsn)
Best regards,
KC.
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To: pgsql-performance@postgresql.org
Cc: kclau60@netvigator.com, jnasby@pervasive.com
Subject: Re: SELECT MIN, MAX took longer time than SELECT
In-Reply-To: <6.2.1.2.0.20060121210512.08cc9310@localhost>
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