From oliveiros.cristina@marktest.pt Mon May  25 13:34:12 2009
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From: "Oliveiros Cristina" <oliveiros.cristina@marktest.pt>
To: <pgsql-sql@postgresql.org>
Cc: <pgsql-novice@postgresql.org>
Subject: Obtaining a limited number of records from a long query
Date: Mon, 25 May 2009 14:32:14 +0100
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Dear List,

Is there any way to force a query to return just a few records?

For ex, returning just the first ten rows from a long ORDER BY query ?

And then, eventually, obtaining the remaining records at a later time, =
or in background?

Thanks in advance for your help,

Best,
Oliveiros
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML><HEAD>
<META content=3D"text/html; charset=3Diso-8859-1" =
http-equiv=3DContent-Type>
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<STYLE></STYLE>
</HEAD>
<BODY bgColor=3D#ffffff>
<DIV><FONT size=3D2 face=3DArial>Dear List,</FONT></DIV>
<DIV><FONT size=3D2 face=3DArial></FONT>&nbsp;</DIV>
<DIV><FONT size=3D2 face=3DArial>Is there any way to force a query to =
return just a=20
few records?</FONT></DIV>
<DIV><FONT size=3D2 face=3DArial></FONT>&nbsp;</DIV>
<DIV><FONT size=3D2 face=3DArial>For ex, returning just the first ten =
rows from a=20
long ORDER BY query ?</FONT></DIV>
<DIV><FONT size=3D2 face=3DArial></FONT>&nbsp;</DIV>
<DIV><FONT size=3D2 face=3DArial>And then, eventually, obtaining the =
remaining=20
records at a later time, or in background?</FONT></DIV>
<DIV><FONT size=3D2 face=3DArial></FONT>&nbsp;</DIV>
<DIV><FONT size=3D2 face=3DArial>Thanks in advance for your =
help,</FONT></DIV>
<DIV><FONT size=3D2 face=3DArial></FONT>&nbsp;</DIV>
<DIV><FONT size=3D2 face=3DArial>Best,</FONT></DIV>
<DIV><FONT size=3D2 face=3DArial>Oliveiros</FONT></DIV></BODY></HTML>

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From lecneri@gmail.com Mon May  25 13:43:14 2009
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References: <020201c9dd3d$372c3f40$ec5a3d0a@marktestcr.marktest.pt>
Date: Mon, 25 May 2009 10:42:24 -0300
Message-ID: <252e1f290905250642w66c6b962k248624b5327be043@mail.gmail.com>
Subject: Re: Obtaining a limited number of records from a long query
From: Luiz Eduardo Cantanhede Neri <lecneri@gmail.com>
To: Oliveiros Cristina <oliveiros.cristina@marktest.pt>
Cc: pgsql-sql@postgresql.org, pgsql-novice@postgresql.org
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Visit http://www.sqlzoo.net/howto/source/z.dir/tip915069/postgres and u'll
get ur awnser and others like from 11th and on.

For now you may try SELECT * FROM cia LIMIT 10

On Mon, May 25, 2009 at 10:32 AM, Oliveiros Cristina <
oliveiros.cristina@marktest.pt> wrote:

>  Dear List,
>
> Is there any way to force a query to return just a few records?
>
> For ex, returning just the first ten rows from a long ORDER BY query ?
>
> And then, eventually, obtaining the remaining records at a later time, or
> in background?
>
> Thanks in advance for your help,
>
> Best,
> Oliveiros
>

--001636499069bfa076046abcc78e
Content-Type: text/html; charset=ISO-8859-1
Content-Transfer-Encoding: quoted-printable

Visit <a href=3D"http://www.sqlzoo.net/howto/source/z.dir/tip915069/postgre=
s">http://www.sqlzoo.net/howto/source/z.dir/tip915069/postgres</a> and u&#3=
9;ll get ur awnser and others like from 11th and on.<br><br>For now you may=
 try SELECT * FROM cia LIMIT 10<br>
<br><div class=3D"gmail_quote">On Mon, May 25, 2009 at 10:32 AM, Oliveiros =
Cristina <span dir=3D"ltr">&lt;<a href=3D"mailto:oliveiros.cristina@marktes=
t.pt">oliveiros.cristina@marktest.pt</a>&gt;</span> wrote:<br><blockquote c=
lass=3D"gmail_quote" style=3D"border-left: 1px solid rgb(204, 204, 204); ma=
rgin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">






<div bgcolor=3D"#ffffff">
<div><font size=3D"2" face=3D"Arial">Dear List,</font></div>
<div><font size=3D"2" face=3D"Arial"></font>=A0</div>
<div><font size=3D"2" face=3D"Arial">Is there any way to force a query to r=
eturn just a=20
few records?</font></div>
<div><font size=3D"2" face=3D"Arial"></font>=A0</div>
<div><font size=3D"2" face=3D"Arial">For ex, returning just the first ten r=
ows from a=20
long ORDER BY query ?</font></div>
<div><font size=3D"2" face=3D"Arial"></font>=A0</div>
<div><font size=3D"2" face=3D"Arial">And then, eventually, obtaining the re=
maining=20
records at a later time, or in background?</font></div>
<div><font size=3D"2" face=3D"Arial"></font>=A0</div>
<div><font size=3D"2" face=3D"Arial">Thanks in advance for your help,</font=
></div>
<div><font size=3D"2" face=3D"Arial"></font>=A0</div>
<div><font size=3D"2" face=3D"Arial">Best,</font></div>
<div><font size=3D"2" face=3D"Arial">Oliveiros</font></div></div>
</blockquote></div><br>

--001636499069bfa076046abcc78e--



From andy-lists@networkmail.eu Mon May  25 13:46:40 2009
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To: Oliveiros Cristina <oliveiros.cristina@marktest.pt>
CC: pgsql-sql@postgresql.org
Subject: Re: Obtaining a limited number of records from a long query
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Hi Oliveiros

Certainly!  What you're looking for is the LIMIT...OFFSET syntax.

Some examples:

SELECT ... LIMIT 10 - return the first 10 records only.
SELECT ... LIMIT 10 OFFSET 10 - return 10 records, starting with record 11.

Manual page:

http://www.postgresql.org/docs/8.3/interactive/queries-limit.html

Regards,
Andy

Oliveiros Cristina wrote:
> Dear List,
>  
> Is there any way to force a query to return just a few records?
>  
> For ex, returning just the first ten rows from a long ORDER BY query ?
>  
> And then, eventually, obtaining the remaining records at a later time, 
> or in background?
>  
> Thanks in advance for your help,
>  
> Best,
> Oliveiros



From oliveiros.cristina@marktest.pt Mon May  25 13:58:14 2009
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Subject: Re: Obtaining a limited number of records from a long query
Date: Mon, 25 May 2009 14:55:54 +0100
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Thanks a million, Andy.

It's precisely what I needed, Indeed!

Best,
Oliveiros

----- Original Message ----- 
From: "Andy Shellam" <andy-lists@networkmail.eu>
To: "Oliveiros Cristina" <oliveiros.cristina@marktest.pt>
Cc: <pgsql-sql@postgresql.org>
Sent: Monday, May 25, 2009 2:45 PM
Subject: Re: [SQL] Obtaining a limited number of records from a long query


> Hi Oliveiros
>
> Certainly!  What you're looking for is the LIMIT...OFFSET syntax.
>
> Some examples:
>
> SELECT ... LIMIT 10 - return the first 10 records only.
> SELECT ... LIMIT 10 OFFSET 10 - return 10 records, starting with record 
> 11.
>
> Manual page:
>
> http://www.postgresql.org/docs/8.3/interactive/queries-limit.html
>
> Regards,
> Andy
>
> Oliveiros Cristina wrote:
>> Dear List,
>>  Is there any way to force a query to return just a few records?
>>  For ex, returning just the first ten rows from a long ORDER BY query ?
>>  And then, eventually, obtaining the remaining records at a later time, 
>> or in background?
>>  Thanks in advance for your help,
>>  Best,
>> Oliveiros
>
> -- 
> Sent via pgsql-sql mailing list (pgsql-sql@postgresql.org)
> To make changes to your subscription:
> http://www.postgresql.org/mailpref/pgsql-sql
> 




From mail@webthatworks.it Mon May  25 14:14:00 2009
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Date: Mon, 25 May 2009 16:13:47 +0200
From: Ivan Sergio Borgonovo <mail@webthatworks.it>
To: <pgsql-sql@postgresql.org>
Subject: Re: Obtaining a limited number of records from a long query
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On Mon, 25 May 2009 14:55:54 +0100
"Oliveiros Cristina" <oliveiros.cristina@marktest.pt> wrote:

> 
> 
> Thanks a million, Andy.
> 
> It's precisely what I needed, Indeed!

Beware: unless you specify an ORDER BY (and you expect no other
record is inserted between one query and the other... or you just
don't care) you may incur in unexpected results.

A query without an order by is not granted to return the result in
the same order.

If you can (same session) you may use cursors.


-- 
Ivan Sergio Borgonovo
http://www.webthatworks.it




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--As of May 25, 2009 2:32:14 PM +0100, Oliveiros Cristina is alleged to 
have said:

> Is there any way to force a query to return just a few records?
>
> For ex, returning just the first ten rows from a long ORDER BY query ?
>
> And then, eventually, obtaining the remaining records at a later time, or
> in background?
>
> Thanks in advance for your help,

--As for the rest, it is mine.

Depending on what you want, either LIMIT and OFFSET or a cursor will help 
you.

<http://www.postgresql.org/docs/8.3/interactive/queries-limit.html>
<http://www.postgresql.org/docs/8.3/interactive/sql-declare.html>

Daniel T. Staal

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From oliveiros.cristina@marktest.pt Mon May  25 14:21:03 2009
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From: "Oliveiros Cristina" <oliveiros.cristina@marktest.pt>
To: "Ivan Sergio Borgonovo" <mail@webthatworks.it>, <pgsql-sql@postgresql.org>
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Subject: Re: Obtaining a limited number of records from a long query
Date: Mon, 25 May 2009 15:20:57 +0100
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Thank you for pointing it out, Ivan.
The query I am trying to restrict output for happens to be an ORDER BY 
query.
Actually I wasn't aware of this detail.
I'll leave a mental note for myself that results might be unexpected for not 
ORDER BY queries

Best,
Oliveiros

----- Original Message ----- 
From: "Ivan Sergio Borgonovo" <mail@webthatworks.it>
To: <pgsql-sql@postgresql.org>
Sent: Monday, May 25, 2009 3:13 PM
Subject: Re: [SQL] Obtaining a limited number of records from a long query


> On Mon, 25 May 2009 14:55:54 +0100
> "Oliveiros Cristina" <oliveiros.cristina@marktest.pt> wrote:
>
>>
>>
>> Thanks a million, Andy.
>>
>> It's precisely what I needed, Indeed!
>
> Beware: unless you specify an ORDER BY (and you expect no other
> record is inserted between one query and the other... or you just
> don't care) you may incur in unexpected results.
>
> A query without an order by is not granted to return the result in
> the same order.
>
> If you can (same session) you may use cursors.
>
>
> -- 
> Ivan Sergio Borgonovo
> http://www.webthatworks.it
>
>
> -- 
> Sent via pgsql-sql mailing list (pgsql-sql@postgresql.org)
> To make changes to your subscription:
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Date: Mon, 25 May 2009 16:56:17 +0200
From: Ivan Sergio Borgonovo <mail@webthatworks.it>
To: pgsql-sql@postgresql.org
Subject: Re: Obtaining a limited number of records from a long query
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On Mon, 25 May 2009 15:20:57 +0100
"Oliveiros Cristina" <oliveiros.cristina@marktest.pt> wrote:

> Thank you for pointing it out, Ivan.
> The query I am trying to restrict output for happens to be an
> ORDER BY query.
> Actually I wasn't aware of this detail.
> I'll leave a mental note for myself that results might be
> unexpected for not ORDER BY queries

a bit more about "unexpected":

- if people insert other rows... and by chance they happen to fall
  before the ones you already retrieved... no matter of the ORDER
  BY, you may "miss" them in the "paginated result".
- without an order by there is no "granted" order. This is not a
  deficiency of PostgreSQL, it is not mandated by sql standard and
  it offers chances for optimisation

The fact that without an order by clause they may return in the same
order... is implementation dependent and Postgresql don't behave
that way or it happens just by chance.

-- 
Ivan Sergio Borgonovo
http://www.webthatworks.it