From: Gnanavel S <s.gnanavel@gmail.com>
To: karim.nassar@acm.org
Cc: pgsql-performance@postgresql.org
Subject: Re: Two queries are better than one?
Date: Fri, 29 Jul 2005 10:08:49 +0530
Message-ID: <eec3b03c05072821386a068a13@mail.gmail.com> (raw)
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<eec3b03c050728211116bafdab@mail.gmail.com>
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On 7/29/05, Karim Nassar <karim.nassar@acm.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?
ok.
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.nassar@acm.org>
>
>
--
with regards,
S.Gnanavel
Satyam Computer Services Ltd.
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Subject: Re: Two queries are better than one?
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