mirror of
https://github.com/postgres/postgres.git
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Fix several <ulink> tags which refer to e-mail addresses
but were missing the "mailto:" prefix. Fix typo. Thanks to Neil Conway <nconway@klamath.dyndns.org> for the heads-up.
This commit is contained in:
Thomas G. Lockhart
parent
f9b2f9bb76
commit
2b6a35f7cd
@ -1,5 +1,5 @@
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<!--
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$Header: /cvsroot/pgsql/doc/src/sgml/datatype.sgml,v 1.32 2000/07/29 18:45:51 tgl Exp $
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$Header: /cvsroot/pgsql/doc/src/sgml/datatype.sgml,v 1.33 2000/08/23 05:59:01 thomas Exp $
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-->
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<chapter id="datatype">
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@ -594,7 +594,7 @@ CREATE TABLE <replaceable class="parameter">tablename</replaceable> (<replaceabl
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<entry>12 bytes</entry>
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<entry>-178000000 years</entry>
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<entry>178000000 years</entry>
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<entry>1 mircosecond</entry>
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<entry>1 microsecond</entry>
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</row>
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<row>
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<entry><type>date</type></entry>
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@ -1,5 +1,5 @@
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<!--
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$Header: /cvsroot/pgsql/doc/src/sgml/datetime.sgml,v 2.10 2000/05/02 20:36:21 thomas Exp $
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$Header: /cvsroot/pgsql/doc/src/sgml/datetime.sgml,v 2.11 2000/08/23 05:59:01 thomas Exp $
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Date/time details
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-->
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@ -629,7 +629,7 @@ Date/time details
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<note>
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<para>
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Contributed by
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<ulink url="jose@sferacarta.com">José Soares</ulink>.
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<ulink url="mailto:jose@sferacarta.com">José Soares</ulink>.
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</para>
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</note>
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@ -1,5 +1,5 @@
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<!--
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||||
$Header: /cvsroot/pgsql/doc/src/sgml/ecpg.sgml,v 1.14 2000/05/02 20:01:51 thomas Exp $
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$Header: /cvsroot/pgsql/doc/src/sgml/ecpg.sgml,v 1.15 2000/08/23 05:59:01 thomas Exp $
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-->
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<chapter>
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@ -32,8 +32,8 @@ $Header: /cvsroot/pgsql/doc/src/sgml/ecpg.sgml,v 1.14 2000/05/02 20:01:51 thomas
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This describes an embedded <acronym>SQL</acronym> in <acronym>C</acronym>
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package for <productname>Postgres</productname>.
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It is written by <ulink url="linus@epact.se">Linus Tolke</ulink>
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and <ulink url="meskes@debian.org">Michael Meskes</ulink>.
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It is written by <ulink url="mailto:linus@epact.se">Linus Tolke</ulink>
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and <ulink url="mailto:meskes@debian.org">Michael Meskes</ulink>.
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<note>
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<para>
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@ -1,119 +1,125 @@
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<!--
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$Header: /cvsroot/pgsql/doc/src/sgml/geqo.sgml,v 1.10 2000/06/28 03:30:53 tgl Exp $
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$Header: /cvsroot/pgsql/doc/src/sgml/geqo.sgml,v 1.11 2000/08/23 05:59:02 thomas Exp $
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Genetic Optimizer
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-->
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<Chapter Id="geqo">
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<DocInfo>
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<Author>
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<FirstName>Martin</FirstName>
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<SurName>Utesch</SurName>
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<Affiliation>
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<Orgname>
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<chapter id="geqo">
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<docinfo>
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<author>
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<firstname>Martin</firstname>
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<surname>Utesch</surname>
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<affiliation>
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<orgname>
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University of Mining and Technology
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</Orgname>
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<Orgdiv>
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</orgname>
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<orgdiv>
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Institute of Automatic Control
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</Orgdiv>
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<Address>
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<City>
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</orgdiv>
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<address>
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<city>
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Freiberg
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</City>
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<Country>
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</city>
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<country>
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Germany
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</Country>
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</Address>
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</Affiliation>
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</Author>
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<Date>1997-10-02</Date>
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</DocInfo>
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</country>
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</address>
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</affiliation>
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</author>
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<date>1997-10-02</date>
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</docinfo>
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<Title>Genetic Query Optimization in Database Systems</Title>
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<title>Genetic Query Optimization in Database Systems</title>
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<Para>
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<Note>
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<Title>Author</Title>
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<Para>
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Written by <ULink url="utesch@aut.tu-freiberg.de">Martin Utesch</ULink>
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<para>
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<note>
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<title>Author</title>
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<para>
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Written by <ulink url="mailto:utesch@aut.tu-freiberg.de">Martin Utesch</ulink>
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for the Institute of Automatic Control at the University of Mining and Technology in Freiberg, Germany.
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</Para>
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</Note>
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</para>
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</note>
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</para>
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<Sect1>
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<Title>Query Handling as a Complex Optimization Problem</Title>
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<sect1>
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<title>Query Handling as a Complex Optimization Problem</title>
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<Para>
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<para>
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Among all relational operators the most difficult one to process and
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optimize is the <FirstTerm>join</FirstTerm>. The number of alternative plans to answer a query
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grows exponentially with the number of <Command>join</Command>s included in it. Further
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optimization effort is caused by the support of a variety of <FirstTerm>join methods</FirstTerm>
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(e.g., nested loop, index scan, merge join in <ProductName>Postgres</ProductName>) to
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process individual <Command>join</Command>s and a diversity of <FirstTerm>indices</FirstTerm> (e.g., r-tree,
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b-tree, hash in <ProductName>Postgres</ProductName>) as access paths for relations.
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optimize is the <firstterm>join</firstterm>. The number of alternative plans to answer a query
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grows exponentially with the number of <command>join</command>s included in it. Further
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optimization effort is caused by the support of a variety of
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<firstterm>join methods</firstterm>
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(e.g., nested loop, index scan, merge join in <productname>Postgres</productname>) to
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process individual <command>join</command>s and a diversity of
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<firstterm>indices</firstterm> (e.g., r-tree,
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b-tree, hash in <productname>Postgres</productname>) as access paths for relations.
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</para>
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<Para>
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The current <ProductName>Postgres</ProductName> optimizer implementation performs a <FirstTerm>near-
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exhaustive search</FirstTerm> over the space of alternative strategies. This query
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<para>
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The current <productname>Postgres</productname> optimizer
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implementation performs a <firstterm>near-
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exhaustive search</firstterm> over the space of alternative strategies. This query
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optimization technique is inadequate to support database application
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domains that involve the need for extensive queries, such as artificial
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intelligence.
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</para>
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<Para>
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<para>
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The Institute of Automatic Control at the University of Mining and
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Technology, in Freiberg, Germany, encountered the described problems as its
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folks wanted to take the <ProductName>Postgres</ProductName> DBMS as the backend for a decision
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folks wanted to take the <productname>Postgres</productname> DBMS as the backend for a decision
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support knowledge based system for the maintenance of an electrical
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power grid. The DBMS needed to handle large <Command>join</Command> queries for the
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power grid. The DBMS needed to handle large <command>join</command> queries for the
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inference machine of the knowledge based system.
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</para>
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<Para>
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<para>
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Performance difficulties within exploring the space of possible query
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plans arose the demand for a new optimization technique being developed.
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</para>
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<Para>
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In the following we propose the implementation of a <FirstTerm>Genetic Algorithm</FirstTerm>
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<para>
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In the following we propose the implementation of a <firstterm>Genetic Algorithm</firstterm>
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as an option for the database query optimization problem.
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</para>
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</sect1>
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<Sect1>
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<Title>Genetic Algorithms (<Acronym>GA</Acronym>)</Title>
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<sect1>
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<title>Genetic Algorithms (<acronym>GA</acronym>)</title>
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<Para>
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The <Acronym>GA</Acronym> is a heuristic optimization method which operates through
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<para>
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The <acronym>GA</acronym> is a heuristic optimization method which operates through
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determined, randomized search. The set of possible solutions for the
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optimization problem is considered as a <FirstTerm>population</FirstTerm> of <FirstTerm>individuals</FirstTerm>.
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optimization problem is considered as a
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<firstterm>erm>popula</firstterm>erm> of <firstterm>individuals</firstterm>.
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The degree of adaption of an individual to its environment is specified
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by its <FirstTerm>fitness</FirstTerm>.
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by its <firstterm>fitness</firstterm>.
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</para>
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<Para>
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<para>
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The coordinates of an individual in the search space are represented
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by <FirstTerm>chromosomes</FirstTerm>, in essence a set of character strings. A <FirstTerm>gene</FirstTerm> is a
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by <firstterm>chromosomes</firstterm>, in essence a set of character
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strings. A <firstterm>gene</firstterm> is a
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subsection of a chromosome which encodes the value of a single parameter
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being optimized. Typical encodings for a gene could be <FirstTerm>binary</FirstTerm> or
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<FirstTerm>integer</FirstTerm>.
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being optimized. Typical encodings for a gene could be <firstterm>binary</firstterm> or
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<firstterm>integer</firstterm>.
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</para>
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<Para>
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Through simulation of the evolutionary operations <FirstTerm>recombination</FirstTerm>,
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<FirstTerm>mutation</FirstTerm>, and <FirstTerm>selection</FirstTerm> new generations of search points are found
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<para>
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Through simulation of the evolutionary operations <firstterm>recombination</firstterm>,
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<firstterm>mutation</firstterm>, and
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<firstterm>selection</firstterm> new generations of search points are found
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that show a higher average fitness than their ancestors.
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</para>
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<Para>
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According to the "comp.ai.genetic" <Acronym>FAQ</Acronym> it cannot be stressed too
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strongly that a <Acronym>GA</Acronym> is not a pure random search for a solution to a
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problem. A <Acronym>GA</Acronym> uses stochastic processes, but the result is distinctly
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<para>
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According to the "comp.ai.genetic" <acronym>FAQ</acronym> it cannot be stressed too
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strongly that a <acronym>GA</acronym> is not a pure random search for a solution to a
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problem. A <acronym>GA</acronym> uses stochastic processes, but the result is distinctly
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non-random (better than random).
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<ProgramListing>
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Structured Diagram of a <Acronym>GA</Acronym>:
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<programlisting>
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Structured Diagram of a <acronym>GA</acronym>:
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---------------------------
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P(t) generation of ancestors at a time t
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@ -140,139 +146,144 @@ P''(t) generation of descendants at a time t
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| +-------------------------------------+
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||||
| | t := t + 1 |
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+===+=====================================+
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</ProgramListing>
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</programlisting>
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</para>
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</sect1>
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<Sect1>
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<Title>Genetic Query Optimization (<Acronym>GEQO</Acronym>) in Postgres</Title>
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<sect1>
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<title>Genetic Query Optimization (<acronym>GEQO</acronym>) in Postgres</title>
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<Para>
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The <Acronym>GEQO</Acronym> module is intended for the solution of the query
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optimization problem similar to a traveling salesman problem (<Acronym>TSP</Acronym>).
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<para>
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The <acronym>GEQO</acronym> module is intended for the solution of the query
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optimization problem similar to a traveling salesman problem (<acronym>TSP</acronym>).
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Possible query plans are encoded as integer strings. Each string
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represents the <Command>join</Command> order from one relation of the query to the next.
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represents the <command>join</command> order from one relation of the query to the next.
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E. g., the query tree
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<ProgramListing>
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<programlisting>
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/\
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/\ 2
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/\ 3
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4 1
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</ProgramListing>
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</programlisting>
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is encoded by the integer string '4-1-3-2',
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which means, first join relation '4' and '1', then '3', and
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then '2', where 1, 2, 3, 4 are relids in <ProductName>Postgres</ProductName>.
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then '2', where 1, 2, 3, 4 are relids in <productname>Postgres</productname>.
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</para>
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<Para>
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Parts of the <Acronym>GEQO</Acronym> module are adapted from D. Whitley's Genitor
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<para>
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Parts of the <acronym>GEQO</acronym> module are adapted from D. Whitley's Genitor
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algorithm.
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</para>
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<Para>
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Specific characteristics of the <Acronym>GEQO</Acronym> implementation in <ProductName>Postgres</ProductName>
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<para>
|
||||
Specific characteristics of the <acronym>GEQO</acronym>
|
||||
implementation in <productname>Postgres</productname>
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are:
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<ItemizedList Mark="bullet" Spacing="compact">
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<ListItem>
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<Para>
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Usage of a <FirstTerm>steady state</FirstTerm> <Acronym>GA</Acronym> (replacement of the least fit
|
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<itemizedlist spacing="compact" mark="bullet">
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<listitem>
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<para>
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Usage of a <firstterm>steady state</firstterm> <acronym>GA</acronym> (replacement of the least fit
|
||||
individuals in a population, not whole-generational replacement)
|
||||
allows fast convergence towards improved query plans. This is
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essential for query handling with reasonable time;
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</Para>
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</ListItem>
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</para>
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</listitem>
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<ListItem>
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<Para>
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Usage of <FirstTerm>edge recombination crossover</FirstTerm> which is especially suited
|
||||
to keep edge losses low for the solution of the <Acronym>TSP</Acronym> by means of a <Acronym>GA</Acronym>;
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||||
</Para>
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||||
</ListItem>
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<listitem>
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||||
<para>
|
||||
Usage of <firstterm>edge recombination crossover</firstterm> which is especially suited
|
||||
to keep edge losses low for the solution of the
|
||||
<acronym>cro</acronym>cronym> by means of a <acronym>GA</acronym>;
|
||||
</para>
|
||||
</listitem>
|
||||
|
||||
<ListItem>
|
||||
<Para>
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<listitem>
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<para>
|
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Mutation as genetic operator is deprecated so that no repair
|
||||
mechanisms are needed to generate legal <Acronym>TSP</Acronym> tours.
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||||
</Para>
|
||||
</ListItem>
|
||||
</ItemizedList>
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mechanisms are needed to generate legal <acronym>TSP</acronym> tours.
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</para>
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||||
</listitem>
|
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</itemizedlist>
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</para>
|
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|
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<Para>
|
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The <Acronym>GEQO</Acronym> module gives the following benefits to the <ProductName>Postgres</ProductName> DBMS
|
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compared to the <ProductName>Postgres</ProductName> query optimizer implementation:
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||||
<para>
|
||||
The <acronym>GEQO</acronym> module gives the following benefits to
|
||||
the <productname>Postgres</productname> DBMS
|
||||
compared to the <productname>Postgres</productname> query optimizer implementation:
|
||||
|
||||
<ItemizedList Mark="bullet" Spacing="compact">
|
||||
<ListItem>
|
||||
<Para>
|
||||
Handling of large <Command>join</Command> queries through non-exhaustive search;
|
||||
</Para>
|
||||
</ListItem>
|
||||
<itemizedlist spacing="compact" mark="bullet">
|
||||
<listitem>
|
||||
<para>
|
||||
Handling of large <command>join</command> queries through non-exhaustive search;
|
||||
</para>
|
||||
</listitem>
|
||||
|
||||
<ListItem>
|
||||
<Para>
|
||||
<listitem>
|
||||
<para>
|
||||
Improved cost size approximation of query plans since no longer
|
||||
plan merging is needed (the <Acronym>GEQO</Acronym> module evaluates the cost for a
|
||||
plan merging is needed (the <acronym>GEQO</acronym> module evaluates the cost for a
|
||||
query plan as an individual).
|
||||
</Para>
|
||||
</ListItem>
|
||||
</ItemizedList>
|
||||
</para>
|
||||
</listitem>
|
||||
</itemizedlist>
|
||||
</para>
|
||||
|
||||
</Sect1>
|
||||
</sect1>
|
||||
|
||||
<Sect1>
|
||||
<Title>Future Implementation Tasks for <ProductName>Postgres</ProductName> <Acronym>GEQO</Acronym></Title>
|
||||
<sect1>
|
||||
<title>Future Implementation Tasks for
|
||||
<productname>ame>Post</productname>ame> <acronym>GEQO</acronym></title>
|
||||
|
||||
<Sect2>
|
||||
<Title>Basic Improvements</Title>
|
||||
<sect2>
|
||||
<title>Basic Improvements</title>
|
||||
|
||||
<Sect3>
|
||||
<Title>Improve genetic algorithm parameter settings</Title>
|
||||
<sect3>
|
||||
<title>Improve genetic algorithm parameter settings</title>
|
||||
|
||||
<Para>
|
||||
In file <FileName>backend/optimizer/geqo/geqo_params.c</FileName>, routines
|
||||
<Function>gimme_pool_size</Function> and <Function>gimme_number_generations</Function>,
|
||||
<para>
|
||||
In file <filename>backend/optimizer/geqo/geqo_params.c</filename>, routines
|
||||
<function>gimme_pool_size</function> and <function>gimme_number_generations</function>,
|
||||
we have to find a compromise for the parameter settings
|
||||
to satisfy two competing demands:
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||||
<ItemizedList Spacing="compact">
|
||||
<ListItem>
|
||||
<Para>
|
||||
<itemizedlist spacing="compact">
|
||||
<listitem>
|
||||
<para>
|
||||
Optimality of the query plan
|
||||
</Para>
|
||||
</ListItem>
|
||||
<ListItem>
|
||||
<Para>
|
||||
</para>
|
||||
</listitem>
|
||||
<listitem>
|
||||
<para>
|
||||
Computing time
|
||||
</Para>
|
||||
</ListItem>
|
||||
</ItemizedList>
|
||||
</para>
|
||||
</listitem>
|
||||
</itemizedlist>
|
||||
</para>
|
||||
</sect3>
|
||||
|
||||
<Sect3>
|
||||
<Title>Find better solution for integer overflow</Title>
|
||||
<sect3>
|
||||
<title>Find better solution for integer overflow</title>
|
||||
|
||||
<Para>
|
||||
In file <FileName>backend/optimizer/geqo/geqo_eval.c</FileName>, routine
|
||||
<Function>geqo_joinrel_size</Function>,
|
||||
the present hack for MAXINT overflow is to set the <ProductName>Postgres</ProductName> integer
|
||||
value of <StructField>rel->size</StructField> to its logarithm.
|
||||
Modifications of <StructName>Rel</StructName> in <FileName>backend/nodes/relation.h</FileName> will
|
||||
surely have severe impacts on the whole <ProductName>Postgres</ProductName> implementation.
|
||||
<para>
|
||||
In file <filename>backend/optimizer/geqo/geqo_eval.c</filename>, routine
|
||||
<function>geqo_joinrel_size</function>,
|
||||
the present hack for MAXINT overflow is to set the <productname>Postgres</productname> integer
|
||||
value of <structfield>rel->size</structfield> to its logarithm.
|
||||
Modifications of <structname>Rel</structname> in <filename>backend/nodes/relation.h</filename> will
|
||||
surely have severe impacts on the whole <productname>Postgres</productname> implementation.
|
||||
</para>
|
||||
</sect3>
|
||||
|
||||
<Sect3>
|
||||
<Title>Find solution for exhausted memory</Title>
|
||||
<sect3>
|
||||
<title>Find solution for exhausted memory</title>
|
||||
|
||||
<Para>
|
||||
<para>
|
||||
Memory exhaustion may occur with more than 10 relations involved in a query.
|
||||
In file <FileName>backend/optimizer/geqo/geqo_eval.c</FileName>, routine
|
||||
<Function>gimme_tree</Function> is recursively called.
|
||||
In file <filename>backend/optimizer/geqo/geqo_eval.c</filename>, routine
|
||||
<function>gimme_tree</function> is recursively called.
|
||||
Maybe I forgot something to be freed correctly, but I dunno what.
|
||||
Of course the <StructName>rel</StructName> data structure of the <Command>join</Command> keeps growing and
|
||||
Of course the <structname>rel</structname> data structure of the
|
||||
<command>join</command> keeps growing and
|
||||
growing the more relations are packed into it.
|
||||
Suggestions are welcome :-(
|
||||
</para>
|
||||
@ -280,89 +291,90 @@ Suggestions are welcome :-(
|
||||
</sect2>
|
||||
|
||||
|
||||
<BIBLIOGRAPHY Id="geqo-biblio">
|
||||
<TITLE>
|
||||
<bibliography id="geqo-biblio">
|
||||
<title>
|
||||
References
|
||||
</TITLE>
|
||||
<PARA>Reference information for <Acronym>GEQ</Acronym> algorithms.
|
||||
</PARA>
|
||||
<BIBLIOENTRY>
|
||||
</title>
|
||||
<para>Reference information for <acronym>GEQ</acronym> algorithms.
|
||||
</para>
|
||||
<biblioentry>
|
||||
|
||||
<BOOKBIBLIO>
|
||||
<TITLE>
|
||||
<bookbiblio>
|
||||
<title>
|
||||
The Hitch-Hiker's Guide to Evolutionary Computation
|
||||
</TITLE>
|
||||
<AUTHORGROUP>
|
||||
<AUTHOR>
|
||||
<FIRSTNAME>Jörg</FIRSTNAME>
|
||||
<SURNAME>Heitkötter</SURNAME>
|
||||
</AUTHOR>
|
||||
<AUTHOR>
|
||||
<FIRSTNAME>David</FIRSTNAME>
|
||||
<SURNAME>Beasley</SURNAME>
|
||||
</AUTHOR>
|
||||
</AUTHORGROUP>
|
||||
<PUBLISHER>
|
||||
<PUBLISHERNAME>
|
||||
</title>
|
||||
<authorgroup>
|
||||
<author>
|
||||
<firstname>Jörg</firstname>
|
||||
<surname>Heitkötter</surname>
|
||||
</author>
|
||||
<author>
|
||||
<firstname>David</firstname>
|
||||
<surname>Beasley</surname>
|
||||
</author>
|
||||
</authorgroup>
|
||||
<publisher>
|
||||
<publishername>
|
||||
InterNet resource
|
||||
</PUBLISHERNAME>
|
||||
</PUBLISHER>
|
||||
<ABSTRACT>
|
||||
<Para>
|
||||
FAQ in <ULink url="news://comp.ai.genetic">comp.ai.genetic</ULink>
|
||||
is available at <ULink url="ftp://ftp.Germany.EU.net/pub/research/softcomp/EC/Welcome.html">Encore</ULink>.
|
||||
</Para>
|
||||
</ABSTRACT>
|
||||
</BOOKBIBLIO>
|
||||
</publishername>
|
||||
</publisher>
|
||||
<abstract>
|
||||
<para>
|
||||
FAQ in <ulink url="news://comp.ai.genetic">comp.ai.genetic</ulink>
|
||||
is available at <ulink
|
||||
url="ftp://ftp.Germany.EU.net/pub/research/softcomp/EC/Welcome.html">Encore</ulink>.
|
||||
</para>
|
||||
</abstract>
|
||||
</bookbiblio>
|
||||
|
||||
<BOOKBIBLIO>
|
||||
<TITLE>
|
||||
<bookbiblio>
|
||||
<title>
|
||||
The Design and Implementation of the Postgres Query Optimizer
|
||||
</TITLE>
|
||||
<AUTHORGROUP>
|
||||
<AUTHOR>
|
||||
<FIRSTNAME>Z.</FIRSTNAME>
|
||||
<SURNAME>Fong</SURNAME>
|
||||
</AUTHOR>
|
||||
</AUTHORGROUP>
|
||||
<PUBLISHER>
|
||||
<PUBLISHERNAME>
|
||||
</title>
|
||||
<authorgroup>
|
||||
<author>
|
||||
<firstname>Z.</firstname>
|
||||
<surname>Fong</surname>
|
||||
</author>
|
||||
</authorgroup>
|
||||
<publisher>
|
||||
<publishername>
|
||||
University of California, Berkeley Computer Science Department
|
||||
</PUBLISHERNAME>
|
||||
</PUBLISHER>
|
||||
<ABSTRACT>
|
||||
<Para>
|
||||
File <FileName>planner/Report.ps</FileName> in the 'postgres-papers' distribution.
|
||||
</Para>
|
||||
</ABSTRACT>
|
||||
</BOOKBIBLIO>
|
||||
</publishername>
|
||||
</publisher>
|
||||
<abstract>
|
||||
<para>
|
||||
File <filename>planner/Report.ps</filename> in the 'postgres-papers' distribution.
|
||||
</para>
|
||||
</abstract>
|
||||
</bookbiblio>
|
||||
|
||||
<BOOKBIBLIO>
|
||||
<TITLE>
|
||||
<bookbiblio>
|
||||
<title>
|
||||
Fundamentals of Database Systems
|
||||
</TITLE>
|
||||
<AUTHORGROUP>
|
||||
<AUTHOR>
|
||||
<FIRSTNAME>R.</FIRSTNAME>
|
||||
<SURNAME>Elmasri</SURNAME>
|
||||
</AUTHOR>
|
||||
<AUTHOR>
|
||||
<FIRSTNAME>S.</FIRSTNAME>
|
||||
<SURNAME>Navathe</SURNAME>
|
||||
</AUTHOR>
|
||||
</AUTHORGROUP>
|
||||
<PUBLISHER>
|
||||
<PUBLISHERNAME>
|
||||
</title>
|
||||
<authorgroup>
|
||||
<author>
|
||||
<firstname>R.</firstname>
|
||||
<surname>Elmasri</surname>
|
||||
</author>
|
||||
<author>
|
||||
<firstname>S.</firstname>
|
||||
<surname>Navathe</surname>
|
||||
</author>
|
||||
</authorgroup>
|
||||
<publisher>
|
||||
<publishername>
|
||||
The Benjamin/Cummings Pub., Inc.
|
||||
</PUBLISHERNAME>
|
||||
</PUBLISHER>
|
||||
</BOOKBIBLIO>
|
||||
</publishername>
|
||||
</publisher>
|
||||
</bookbiblio>
|
||||
|
||||
</BIBLIOENTRY>
|
||||
</BIBLIOGRAPHY>
|
||||
</biblioentry>
|
||||
</bibliography>
|
||||
|
||||
</sect1>
|
||||
</Chapter>
|
||||
</chapter>
|
||||
|
||||
<!-- Keep this comment at the end of the file
|
||||
Local variables:
|
||||
|
||||
@ -163,7 +163,7 @@ SELECT am.amname AS acc_name,
|
||||
<title>Author</title>
|
||||
<para>
|
||||
Written by
|
||||
<ulink url="herouth@oumail.openu.ac.il">Herouth Maoz</ulink>
|
||||
<ulink url="mailto:herouth@oumail.openu.ac.il">Herouth Maoz</ulink>
|
||||
This originally appeared on the User's Mailing List on 1998-03-02
|
||||
in response to the question:
|
||||
"What is the difference between PRIMARY KEY and UNIQUE constraints?".
|
||||
@ -328,7 +328,7 @@ CREATE MEMSTORE ON <table> COLUMNS <cols>
|
||||
<title>Author</title>
|
||||
<para>
|
||||
This is from a reply to a question on the e-mail list
|
||||
by <ulink url="aoki@CS.Berkeley.EDU">Paul M. Aoki</ulink>
|
||||
by <ulink url="mailto:aoki@CS.Berkeley.EDU">Paul M. Aoki</ulink>
|
||||
on 1998-08-11.
|
||||
<!--
|
||||
Paul M. Aoki | University of California at Berkeley
|
||||
|
||||
@ -1,5 +1,5 @@
|
||||
<!--
|
||||
$Header: /cvsroot/pgsql/doc/src/sgml/Attic/jdbc.sgml,v 1.10 2000/03/31 03:27:40 thomas Exp $
|
||||
$Header: /cvsroot/pgsql/doc/src/sgml/Attic/jdbc.sgml,v 1.11 2000/08/23 05:59:02 thomas Exp $
|
||||
-->
|
||||
|
||||
<chapter id="jdbc">
|
||||
@ -9,7 +9,7 @@ $Header: /cvsroot/pgsql/doc/src/sgml/Attic/jdbc.sgml,v 1.10 2000/03/31 03:27:40
|
||||
<note>
|
||||
<title>Author</title>
|
||||
<para>
|
||||
Written by <ulink url="peter@retep.org.uk">Peter T. Mount</ulink>, the
|
||||
Written by <ulink url="mailto:peter@retep.org.uk">Peter T. Mount</ulink>, the
|
||||
author of the <acronym>JDBC</acronym> driver.
|
||||
</para>
|
||||
</note>
|
||||
|
||||
@ -1,8 +1,14 @@
|
||||
<!--
|
||||
$Header: /cvsroot/pgsql/doc/src/sgml/Attic/keys.sgml,v 1.3 1998/12/29 02:24:16 thomas Exp $
|
||||
$Header: /cvsroot/pgsql/doc/src/sgml/Attic/keys.sgml,v 1.4 2000/08/23 05:59:02 thomas Exp $
|
||||
Indices and Keys
|
||||
|
||||
$Log: keys.sgml,v $
|
||||
Revision 1.4 2000/08/23 05:59:02 thomas
|
||||
Fix several <ulink> tags which refer to e-mail addresses
|
||||
but were missing the "mailto:" prefix.
|
||||
Fix typo.
|
||||
Thanks to Neil Conway <nconway@klamath.dyndns.org> for the heads-up.
|
||||
|
||||
Revision 1.3 1998/12/29 02:24:16 thomas
|
||||
Clean up to ensure tag completion as required by the newest versions
|
||||
of Norm's Modular Style Sheets and jade/docbook.
|
||||
@ -18,7 +24,7 @@ Will go into the User's Guide.
|
||||
|
||||
-->
|
||||
|
||||
<chapter id="keys">
|
||||
<chapter>
|
||||
<docinfo>
|
||||
<authorgroup>
|
||||
<author>
|
||||
@ -29,26 +35,26 @@ Will go into the User's Guide.
|
||||
<date>1998-03-02</date>
|
||||
</docinfo>
|
||||
|
||||
<Title>Indices and Keys</Title>
|
||||
<title>Indices and Keys</title>
|
||||
|
||||
<Note>
|
||||
<Title>Author</Title>
|
||||
<Para>
|
||||
<note>
|
||||
<title>Author</title>
|
||||
<para>
|
||||
Written by
|
||||
<ULink url="herouth@oumail.openu.ac.il">Herouth Maoz</ULink>
|
||||
</Para>
|
||||
</Note>
|
||||
<ulink url="mailto:herouth@oumail.openu.ac.il">Herouth Maoz</ulink>
|
||||
</para>
|
||||
</note>
|
||||
|
||||
<Note>
|
||||
<Title>Editor's Note</Title>
|
||||
<Para>
|
||||
<note>
|
||||
<title>Editor's Note</title>
|
||||
<para>
|
||||
This originally appeared on the mailing list
|
||||
in response to the question:
|
||||
"What is the difference between PRIMARY KEY and UNIQUE constraints?".
|
||||
</Para>
|
||||
</Note>
|
||||
</para>
|
||||
</note>
|
||||
|
||||
<ProgramListing>
|
||||
<programlisting>
|
||||
Subject: Re: [QUESTIONS] PRIMARY KEY | UNIQUE
|
||||
|
||||
What's the difference between:
|
||||
@ -59,99 +65,100 @@ Subject: Re: [QUESTIONS] PRIMARY KEY | UNIQUE
|
||||
- Is this an alias?
|
||||
- If PRIMARY KEY is already unique, then why
|
||||
is there another kind of key named UNIQUE?
|
||||
</ProgramListing>
|
||||
</programlisting>
|
||||
|
||||
<Para>
|
||||
<para>
|
||||
A primary key is the field(s) used to identify a specific row. For example,
|
||||
Social Security numbers identifying a person.
|
||||
</Para>
|
||||
<Para>
|
||||
</para>
|
||||
<para>
|
||||
A simply UNIQUE combination of fields has nothing to do with identifying
|
||||
the row. It's simply an integrity constraint. For example, I have
|
||||
collections of links. Each collection is identified by a unique number,
|
||||
which is the primary key. This key is used in relations.
|
||||
</Para>
|
||||
<Para>
|
||||
</para>
|
||||
<para>
|
||||
However, my application requires that each collection will also have a
|
||||
unique name. Why? So that a human being who wants to modify a collection
|
||||
will be able to identify it. It's much harder to know, if you have two
|
||||
collections named "Life Science", the the one tagged 24433 is the one you
|
||||
need, and the one tagged 29882 is not.
|
||||
</Para>
|
||||
<Para>
|
||||
</para>
|
||||
<para>
|
||||
So, the user selects the collection by its name. We therefore make sure,
|
||||
withing the database, that names are unique. However, no other table in the
|
||||
database relates to the collections table by the collection Name. That
|
||||
would be very inefficient.
|
||||
</Para>
|
||||
<Para>
|
||||
</para>
|
||||
<para>
|
||||
Moreover, despite being unique, the collection name does not actually
|
||||
define the collection! For example, if somebody decided to change the name
|
||||
of the collection from "Life Science" to "Biology", it will still be the
|
||||
same collection, only with a different name. As long as the name is unique,
|
||||
that's OK.
|
||||
</Para>
|
||||
<Para>
|
||||
</para>
|
||||
<para>
|
||||
So:
|
||||
|
||||
<itemizedlist>
|
||||
<ListItem>
|
||||
<Para>
|
||||
<listitem>
|
||||
<para>
|
||||
Primary key:
|
||||
<itemizedList Mark="bullet" Spacing="compact">
|
||||
<ListItem>
|
||||
<Para>
|
||||
<itemizedlist>
|
||||
<listitem>
|
||||
<para>
|
||||
Is used for identifying the row and relating to it.
|
||||
</Para>
|
||||
</ListItem>
|
||||
<ListItem>
|
||||
<Para>
|
||||
</para>
|
||||
</listitem>
|
||||
<listitem>
|
||||
<para>
|
||||
Is impossible (or hard) to update.
|
||||
</Para>
|
||||
</ListItem>
|
||||
<ListItem>
|
||||
<Para>
|
||||
</para>
|
||||
</listitem>
|
||||
<listitem>
|
||||
<para>
|
||||
Should not allow NULLs.
|
||||
</Para>
|
||||
</ListItem>
|
||||
</para>
|
||||
</listitem>
|
||||
</itemizedlist>
|
||||
</para>
|
||||
</listitem>
|
||||
|
||||
<ListItem>
|
||||
<Para>
|
||||
<listitem>
|
||||
<para>
|
||||
Unique field(s):
|
||||
<itemizedlist Mark="bullet" Spacing="compact">
|
||||
<ListItem>
|
||||
<Para>
|
||||
<itemizedlist>
|
||||
<listitem>
|
||||
<para>
|
||||
Are used as an alternative access to the row.
|
||||
</Para>
|
||||
</ListItem>
|
||||
<ListItem>
|
||||
<Para>
|
||||
</para>
|
||||
</listitem>
|
||||
<listitem>
|
||||
<para>
|
||||
Are updateable, so long as they are kept unique.
|
||||
</Para>
|
||||
</ListItem>
|
||||
<ListItem>
|
||||
<Para>
|
||||
</para>
|
||||
</listitem>
|
||||
<listitem>
|
||||
<para>
|
||||
NULLs are acceptable.
|
||||
</Para>
|
||||
</ListItem>
|
||||
</para>
|
||||
</listitem>
|
||||
</itemizedlist>
|
||||
</para>
|
||||
</listitem>
|
||||
</itemizedlist>
|
||||
</para>
|
||||
|
||||
<Para>
|
||||
As for why no non-unique keys are defined explicitly in standard <acronym>SQL</acronym> syntax?
|
||||
<para>
|
||||
As for why no non-unique keys are defined explicitly in standard
|
||||
<acronym>SQL</acronym> syntax?
|
||||
Well, you
|
||||
must understand that indices are implementation-dependent. <acronym>SQL</acronym> does not
|
||||
define the implementation, merely the relations between data in the
|
||||
database. <productname>Postgres</productname> does allow non-unique indices, but indices
|
||||
used to enforce <acronym>SQL</acronym> keys are always unique.
|
||||
</Para>
|
||||
<Para>
|
||||
</para>
|
||||
<para>
|
||||
Thus, you may query a table by any combination of its columns, despite the
|
||||
fact that you don't have an index on these columns. The indexes are merely
|
||||
an implementational aid which each <acronym>RDBMS</acronym> offers you, in order to cause
|
||||
@ -162,22 +169,39 @@ have a special command, for example
|
||||
CREATE MEMSTORE ON <table> COLUMNS <cols>
|
||||
</programlisting>
|
||||
(this is not an existing command, just an example).
|
||||
</Para>
|
||||
<Para>
|
||||
</para>
|
||||
<para>
|
||||
In fact, when you create a primary key or a unique combination of fields,
|
||||
nowhere in the <acronym>SQL</acronym> specification does it say that an index is created, nor that
|
||||
the retrieval of data by the key is going to be more efficient than a
|
||||
sequential scan!
|
||||
</Para>
|
||||
<Para>
|
||||
</para>
|
||||
<para>
|
||||
So, if you want to use a combination of fields which is not unique as a
|
||||
secondary key, you really don't have to specify anything - just start
|
||||
retrieving by that combination! However, if you want to make the retrieval
|
||||
efficient, you'll have to resort to the means your <acronym>RDBMS</acronym> provider gives you
|
||||
- be it an index, my imaginary MEMSTORE command, or an intelligent <acronym>RDBMS</acronym>
|
||||
- be it an index, my imaginary MEMSTORE command, or an intelligent
|
||||
<acronym>RDBMS</acronym>
|
||||
which creates indices without your knowledge based on the fact that you have
|
||||
sent it many queries based on a specific combination of keys... (It learns
|
||||
from experience).
|
||||
</Para>
|
||||
</para>
|
||||
</chapter>
|
||||
|
||||
<!-- Keep this comment at the end of the file
|
||||
Local variables:
|
||||
mode:sgml
|
||||
sgml-omittag:nil
|
||||
sgml-shorttag:t
|
||||
sgml-minimize-attributes:nil
|
||||
sgml-always-quote-attributes:t
|
||||
sgml-indent-step:1
|
||||
sgml-indent-data:t
|
||||
sgml-parent-document:nil
|
||||
sgml-default-dtd-file:"./reference.ced"
|
||||
sgml-exposed-tags:nil
|
||||
sgml-local-catalogs:("/usr/lib/sgml/catalog")
|
||||
sgml-local-ecat-files:nil
|
||||
End:
|
||||
--></book>
|
||||
|
||||
@ -1,5 +1,5 @@
|
||||
<!--
|
||||
$Header: /cvsroot/pgsql/doc/src/sgml/ref/ecpg-ref.sgml,v 1.2 2000/03/31 06:17:52 thomas Exp $
|
||||
$Header: /cvsroot/pgsql/doc/src/sgml/ref/ecpg-ref.sgml,v 1.3 2000/08/23 05:59:11 thomas Exp $
|
||||
Postgres documentation
|
||||
-->
|
||||
|
||||
@ -135,11 +135,11 @@ ecpg [ -v ] [ -t ] [ -I include-path ] [ -o outfile ] file1 [ file2 ] [ ... ]
|
||||
</para>
|
||||
|
||||
<para>
|
||||
<ulink url="linus@epact.se">Linus Tolke</ulink> was the
|
||||
<ulink url="mailto:linus@epact.se">Linus Tolke</ulink> was the
|
||||
original author of <application>ecpg</application> (up to version 0.2).
|
||||
<ulink url="meskes@debian.org">Michael Meskes</ulink>
|
||||
<ulink url="mailto:meskes@debian.org">Michael Meskes</ulink>
|
||||
is the current author and maintainer of <application>ecpg</application>.
|
||||
<ulink url="tomg@q8.nrnet.org">Thomas Good</ulink>
|
||||
<ulink url="mailto:tomg@q8.nrnet.org">Thomas Good</ulink>
|
||||
is the author of the last revision of the ecpg man page, on which
|
||||
this document is based.
|
||||
</para>
|
||||
|
||||
@ -1,5 +1,5 @@
|
||||
<!--
|
||||
$Header: /cvsroot/pgsql/doc/src/sgml/ref/insert.sgml,v 1.7 2000/03/27 17:14:43 thomas Exp $
|
||||
$Header: /cvsroot/pgsql/doc/src/sgml/ref/insert.sgml,v 1.8 2000/08/23 05:59:11 thomas Exp $
|
||||
Postgres documentation
|
||||
-->
|
||||
|
||||
@ -20,20 +20,20 @@ Postgres documentation
|
||||
</refnamediv>
|
||||
<refsynopsisdiv>
|
||||
<refsynopsisdivinfo>
|
||||
<date>1999-07-20</date>
|
||||
<date>2000-08-08</date>
|
||||
</refsynopsisdivinfo>
|
||||
<synopsis>
|
||||
INSERT INTO <replaceable class="PARAMETER">table</replaceable> [ ( <replaceable class="PARAMETER">column</replaceable> [, ...] ) ]
|
||||
{ VALUES ( <replaceable class="PARAMETER">expression</replaceable> [, ...] ) | SELECT <replaceable class="PARAMETER">query</replaceable> }
|
||||
{ DEFAULT VALUES | VALUES ( <replaceable class="PARAMETER">expression</replaceable> [, ...] ) | SELECT <replaceable class="PARAMETER">query</replaceable> }
|
||||
</synopsis>
|
||||
|
||||
<refsect2 id="R2-SQL-INSERT-1">
|
||||
<refsect2info>
|
||||
<date>1998-09-23</date>
|
||||
</refsect2info>
|
||||
<title>
|
||||
Inputs
|
||||
</title>
|
||||
|
||||
<para>
|
||||
|
||||
<variablelist>
|
||||
@ -45,6 +45,7 @@ INSERT INTO <replaceable class="PARAMETER">table</replaceable> [ ( <replaceable
|
||||
</para>
|
||||
</listitem>
|
||||
</varlistentry>
|
||||
|
||||
<varlistentry>
|
||||
<term><replaceable class="PARAMETER">column</replaceable></term>
|
||||
<listitem>
|
||||
@ -54,6 +55,16 @@ INSERT INTO <replaceable class="PARAMETER">table</replaceable> [ ( <replaceable
|
||||
</listitem>
|
||||
</varlistentry>
|
||||
|
||||
<varlistentry>
|
||||
<term>DEFAULT VALUES</term>
|
||||
<listitem>
|
||||
<para>
|
||||
All columns will be filled by NULLs or by values specified
|
||||
when the table was created using DEFAULT clauses.
|
||||
</para>
|
||||
</listitem>
|
||||
</varlistentry>
|
||||
|
||||
<varlistentry>
|
||||
<term><replaceable class="PARAMETER">expression</replaceable></term>
|
||||
<listitem>
|
||||
@ -79,7 +90,6 @@ INSERT INTO <replaceable class="PARAMETER">table</replaceable> [ ( <replaceable
|
||||
|
||||
<refsect2 id="R2-SQL-INSERT-2">
|
||||
<refsect2info>
|
||||
<date>1998-09-23</date>
|
||||
</refsect2info>
|
||||
<title>
|
||||
Outputs
|
||||
@ -118,7 +128,6 @@ INSERT 0 <replaceable>#</replaceable>
|
||||
|
||||
<refsect1 id="R1-SQL-INSERT-1">
|
||||
<refsect1info>
|
||||
<date>1998-09-02</date>
|
||||
</refsect1info>
|
||||
<title>
|
||||
Description
|
||||
@ -217,7 +226,6 @@ INSERT INTO tictactoe (game, board)
|
||||
|
||||
<refsect2 id="R2-SQL-INSERT-4">
|
||||
<refsect2info>
|
||||
<date>1998-09-23</date>
|
||||
</refsect2info>
|
||||
<title>
|
||||
SQL92
|
||||
|
||||
Loading…
x
Reference in New Issue
Block a user