From 25deba3141ecc2d29422e7cd06d0efe0a1d94be1 Mon Sep 17 00:00:00 2001 From: Bruce Momjian Date: Tue, 1 Feb 2005 01:36:13 +0000 Subject: [PATCH] Update LIMIT/FETCH FAQ item. --- doc/FAQ | 23 ++++++++--------------- doc/src/FAQ/FAQ.html | 29 +++++++++++------------------ 2 files changed, 19 insertions(+), 33 deletions(-) diff --git a/doc/FAQ b/doc/FAQ index 884a9e7aa5..c092e10b9c 100644 --- a/doc/FAQ +++ b/doc/FAQ @@ -1,7 +1,7 @@ Frequently Asked Questions (FAQ) for PostgreSQL - Last updated: Mon Jan 31 19:18:44 EST 2005 + Last updated: Mon Jan 31 20:35:58 EST 2005 Current maintainer: Bruce Momjian (pgman@candle.pha.pa.us) @@ -445,17 +445,13 @@ PostgreSQL releases? The PostgreSQL team makes only small changes between minor releases, - so upgrading from 7.2 to 7.2.1 does not require a dump and restore. - However, major releases (e.g. from 7.2 to 7.3) often change the + so upgrading from 7.4 to 7.4.1 does not require a dump and restore. + However, major releases (e.g. from 7.3 to 7.4) often change the internal format of system tables and data files. These changes are - often complex, so we don't maintain backward compatability for data + often complex, so we don't maintain backward compatibility for data files. A dump outputs data in a generic format that can then be loaded in using the new internal format. - In releases where the on-disk format does not change, the pg_upgrade - script can be used to upgrade without a dump/restore. The release - notes mention whether pg_upgrade is available for the release. - 3.8) What computer hardware should I use? Because PC hardware is mostly compatible, people tend to believe that @@ -471,13 +467,10 @@ 4.1) How do I SELECT only the first few rows of a query? A random row? - See the FETCH manual page, or use SELECT ... LIMIT.... - - The entire query may have to be evaluated, even if you only want the - first few rows. Consider using a query that has an ORDER BY. If there - is an index that matches the ORDER BY, PostgreSQL may be able to - evaluate only the first few records requested, or the entire query may - have to be evaluated until the desired rows have been generated. + To retrieve only a few rows, if you know at the number of rows needed + at the time of the SELECT use LIMIT . If an index matches the ORDER BY + it is possible the entire query does not have to be executed. If you + don't know the number of rows at SELECT time, use a cursor and FETCH. To SELECT a random row, use: SELECT col diff --git a/doc/src/FAQ/FAQ.html b/doc/src/FAQ/FAQ.html index 4c8a9a9ab2..1385d59012 100644 --- a/doc/src/FAQ/FAQ.html +++ b/doc/src/FAQ/FAQ.html @@ -10,7 +10,7 @@ alink="#0000ff">

Frequently Asked Questions (FAQ) for PostgreSQL

-

Last updated: Mon Jan 31 19:18:44 EST 2005

+

Last updated: Mon Jan 31 20:35:58 EST 2005

Current maintainer: Bruce Momjian (pgman@candle.pha.pa.us) @@ -590,18 +590,13 @@ to upgrade between major PostgreSQL releases?

The PostgreSQL team makes only small changes between minor releases, - so upgrading from 7.2 to 7.2.1 does not require a dump and restore. - However, major releases (e.g. from 7.2 to 7.3) often change the internal + so upgrading from 7.4 to 7.4.1 does not require a dump and restore. + However, major releases (e.g. from 7.3 to 7.4) often change the internal format of system tables and data files. These changes are often complex, - so we don't maintain backward compatability for data files. A dump outputs + so we don't maintain backward compatibility for data files. A dump outputs data in a generic format that can then be loaded in using the new internal format.

-

In releases where the on-disk format does not change, the - pg_upgrade script can be used to upgrade without a dump/restore. - The release notes mention whether pg_upgrade is available for the - release.

-

3.8) What computer hardware should I use?

Because PC hardware is mostly compatible, people tend to believe that @@ -619,15 +614,13 @@

4.1) How do I SELECT only the first few rows of a query? A random row?

-

See the FETCH manual page, or use - SELECT ... LIMIT....

- -

The entire query may have to be evaluated, even if you only want - the first few rows. Consider using a query that has an ORDER - BY. If there is an index that matches the ORDER - BY, PostgreSQL may be able to evaluate only the first few - records requested, or the entire query may have to be evaluated - until the desired rows have been generated.

+

To retrieve only a few rows, if you know at the number of rows + needed at the time of the SELECT use + LIMIT . If an index matches the ORDER + BY it is possible the entire query does not have to be + executed. If you don't know the number of rows at + SELECT time, use a cursor and + FETCH.

To SELECT a random row, use: 

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