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Message-ID: <eec3b03c05072821386a068a13@mail.gmail.com>
Date: Fri, 29 Jul 2005 10:08:49 +0530
From: Gnanavel S <s.gnanavel@gmail.com>
Reply-To: Gnanavel S <s.gnanavel@gmail.com>
To: karim.nassar@acm.org
Subject: Re: Two queries are better than one?
Cc: pgsql-performance@postgresql.org
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On 7/29/05, Karim Nassar <karim.nassar@acm.org> wrote:
>=20
> On Fri, 2005-07-29 at 09:41 +0530, Gnanavel S wrote:
>=20
> >
> > Joined:
> >
> > test=3D> explain analyze
> > test-> SELECT cli_name,order.*
> > test-> FROM order
> > test-> JOIN client ON (ord_client =3D cli_code)
> > test-> WHERE ord_batch=3D'343B' AND
> > ord_id=3D'12-645';
> >
> > where is the cli_code condition in the above query?
>=20
> 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.
>=20
> Clearer?


ok.

Reason might be comparing with a literal value (previous case) is cheaper=
=20
than comparing with column(as it has to be evaluated). But with the previou=
s=20
case getting and assigning the cli_code in the application and executing in=
=20
db will be time consuming as it includes IPC cost.

--
> Karim Nassar <karim.nassar@acm.org>
>=20
>=20


--=20
with regards,
S.Gnanavel
Satyam Computer Services Ltd.

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<br><br><div><span class=3D"gmail_quote">On 7/29/05, <b class=3D"gmail_send=
ername">Karim Nassar</b> &lt;<a href=3D"mailto:karim.nassar@acm.org">karim.=
nassar@acm.org</a>&gt; wrote:</span><blockquote class=3D"gmail_quote" style=
=3D"border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; p=
adding-left: 1ex;">
On Fri, 2005-07-29 at 09:41 +0530, Gnanavel S wrote:<br><br>&gt;<br>&gt;&nb=
sp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Joined:<br>&gt;<br>&gt;&nbsp;=
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; test=3D&gt; explain analyze<br>&=
gt;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; test-&gt;&nbsp;&nbsp;&n=
bsp;&nbsp;SELECT cli_name,order.*<br>&gt;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbs=
p;&nbsp;&nbsp;
test-&gt;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;=
&nbsp;&nbsp;&nbsp;
FROM order<br>&gt;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
test-&gt;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;=
&nbsp;&nbsp;&nbsp;
JOIN client ON (ord_client =3D cli_code)<br>&gt;&nbsp;&nbsp;&nbsp;&nbsp;&nb=
sp;&nbsp;&nbsp;&nbsp;
test-&gt;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;=
&nbsp;&nbsp;&nbsp;WHERE
ord_batch=3D'343B' AND<br>&gt;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nb=
sp; ord_id=3D'12-645';<br>&gt;<br>&gt; where is the cli_code condition in t=
he above query?<br><br>I don't understand the question. ord_client is the c=
lient code, and<br>cli_code is the client code, for their respective tables=
. batch/id is
<br>unique, so there is only one record from order, and only one client to<=
br>associate.<br><br>Clearer?</blockquote><div><br>
ok.<br>
<br>
&nbsp;Reason might be comparing with a literal value (previous case) is
cheaper than comparing with column(as it has to be evaluated).&nbsp;
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.<br>
<br>
</div><blockquote class=3D"gmail_quote" style=3D"border-left: 1px solid rgb=
(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">--<br>Karim=
 Nassar &lt;<a href=3D"mailto:karim.nassar@acm.org">karim.nassar@acm.org</a=
>
&gt;<br><br></blockquote></div><br><br clear=3D"all"><br>-- <br>with regard=
s,<br>S.Gnanavel<br>Satyam Computer Services Ltd.

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