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author | Bruce Momjian <bruce@momjian.us> | 2005-02-01 01:36:13 +0000 |
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committer | Bruce Momjian <bruce@momjian.us> | 2005-02-01 01:36:13 +0000 |
commit | 25deba3141ecc2d29422e7cd06d0efe0a1d94be1 (patch) | |
tree | ea6c95773c96e17c4c050bc0d448b6464cb63285 | |
parent | 0a92c58b7c4d556b1cfc6a0b557cc32250437c9e (diff) | |
download | postgresql-25deba3141ecc2d29422e7cd06d0efe0a1d94be1.tar.gz postgresql-25deba3141ecc2d29422e7cd06d0efe0a1d94be1.zip |
Update LIMIT/FETCH FAQ item.
-rw-r--r-- | doc/FAQ | 23 | ||||
-rw-r--r-- | doc/src/FAQ/FAQ.html | 29 |
2 files changed, 19 insertions, 33 deletions
@@ -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 4c8a9a9ab2a..1385d590127 100644 --- a/doc/src/FAQ/FAQ.html +++ b/doc/src/FAQ/FAQ.html @@ -10,7 +10,7 @@ alink="#0000ff"> <H1>Frequently Asked Questions (FAQ) for PostgreSQL</H1> - <P>Last updated: Mon Jan 31 19:18:44 EST 2005</P> + <P>Last updated: Mon Jan 31 20:35:58 EST 2005</P> <P>Current maintainer: Bruce Momjian (<A href= "mailto:pgman@candle.pha.pa.us">pgman@candle.pha.pa.us</A>) @@ -590,18 +590,13 @@ to upgrade between major PostgreSQL releases?</H4> <P>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.</P> - <P>In releases where the on-disk format does not change, the - <I>pg_upgrade</I> script can be used to upgrade without a dump/restore. - The release notes mention whether <I>pg_upgrade</I> is available for the - release.</P> - <H4><A name="3.8">3.8</A>) What computer hardware should I use?</H4> <P>Because PC hardware is mostly compatible, people tend to believe that @@ -619,15 +614,13 @@ <H4><A name="4.1">4.1</A>) How do I <SMALL>SELECT</SMALL> only the first few rows of a query? A random row?</H4> - <P>See the <SMALL>FETCH</SMALL> manual page, or use - <SMALL>SELECT</SMALL> ... <SMALL>LIMIT</SMALL>....</P> - - <P>The entire query may have to be evaluated, even if you only want - the first few rows. Consider using a query that has an <SMALL>ORDER - BY</SMALL>. If there is an index that matches the <SMALL>ORDER - BY</SMALL>, 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.</P> + <P>To retrieve only a few rows, if you know at the number of rows + needed at the time of the <SMALL>SELECT</SMALL> use + <SMALL>LIMIT</SMALL> . If an index matches the <SMALL>ORDER + BY</SMALL> it is possible the entire query does not have to be + executed. If you don't know the number of rows at + <SMALL>SELECT</SMALL> time, use a cursor and + <SMALL>FETCH</SMALL>.</P> <P>To <SMALL>SELECT</SMALL> a random row, use: <PRE> |