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Re: Two queries are better than one?

From: Gnanavel S <s(dot)gnanavel(at)gmail(dot)com>
To: karim(dot)nassar(at)acm(dot)org
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: Two queries are better than one?
Date: 2005-07-29 04:38:49
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-performance
On 7/29/05, Karim Nassar <karim(dot)nassar(at)acm(dot)org> wrote:
> On Fri, 2005-07-29 at 09:41 +0530, Gnanavel S wrote:
> >
> > Joined:
> >
> > test=> explain analyze
> > test-> SELECT cli_name,order.*
> > test-> FROM order
> > test-> JOIN client ON (ord_client = cli_code)
> > test-> WHERE ord_batch='343B' AND
> > ord_id='12-645';
> >
> > where is the cli_code condition in the above query?
> I don't understand the question. ord_client is the client code, and
> cli_code is the client code, for their respective tables. batch/id is
> unique, so there is only one record from order, and only one client to
> associate.
> Clearer?


Reason might be comparing with a literal value (previous case) is cheaper 
than comparing with column(as it has to be evaluated). But with the previous 
case getting and assigning the cli_code in the application and executing in 
db will be time consuming as it includes IPC cost.

> Karim Nassar <karim(dot)nassar(at)acm(dot)org>

with regards,
Satyam Computer Services Ltd.

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