Thomas G. Lockhart
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<!--
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$Header: /cvsroot/pgsql/doc/src/sgml/advanced.sgml,v 1.10 2000/04/07 13:30:58 thomas Exp $
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$Header: /cvsroot/pgsql/doc/src/sgml/advanced.sgml,v 1.11 2000/04/11 05:39:06 thomas Exp $
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-->
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<chapter id="advanced">
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@ -234,105 +234,6 @@ SELECT SAL_EMP.schedule[1:2][1:1]
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</sect2>
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</sect1>
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<!--
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We haven't had Time Travel for two or three years, so let's stop
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mentioning it. - thomas 2000-04-02
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<sect1>
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<title>Time Travel</title>
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<para>
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As of <productname>Postgres</productname> v6.2, <emphasis>time
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travel is no longer supported</emphasis>. There are
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several reasons for this: performance impact, storage size, and a
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pg_time file which grows
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toward infinite size in a short period of time.
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</para>
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<para>
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New features such as triggers allow one to mimic the behavior of
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time travel when desired, without
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incurring the overhead when it is not needed (for most users, this
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is most of the time).
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See examples in the <filename>contrib</filename> directory for
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more information.
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</para>
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<note>
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<title>Time travel is deprecated</title>
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<para>
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The remaining text in this section is retained only until it can
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be rewritten in the context
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of new techniques to accomplish the same purpose.
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Volunteers? - thomas 1998-01-12
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</para>
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</note>
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<para>
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<productname>Postgres</productname> supports the notion of time
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travel. This feature
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allows a user to run historical queries. For
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example, to find the current population of Mariposa
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city, one would query:
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<programlisting>
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SELECT * FROM cities WHERE name = 'Mariposa';
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+---------+------------+----------+
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|name | population | altitude |
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+---------+------------+----------+
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|Mariposa | 1320 | 1953 |
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+---------+------------+----------+
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</programlisting>
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<productname>Postgres</productname> will automatically find the
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version of Mariposa's
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record valid at the current time.
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One can also give a time range. For example to see the
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past and present populations of Mariposa, one would
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query:
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<programlisting>
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SELECT name, population
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FROM cities['epoch', 'now']
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WHERE name = 'Mariposa';
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</programlisting>
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where "epoch" indicates the beginning of the system
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clock.
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<note>
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<para>
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On Unix systems, this is always midnight, January 1, 1970 GMT.
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</para>
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</note>
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</para>
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<para>
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If you have executed all of the examples so
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far, then the above query returns:
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<programlisting>
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+---------+------------+
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|name | population |
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+---------+------------+
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|Mariposa | 1200 |
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+---------+------------+
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|Mariposa | 1320 |
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+---------+------------+
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</programlisting>
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</para>
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<para>
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The default beginning of a time range is the earliest
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time representable by the system and the default end is
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the current time; thus, the above time range can be
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abbreviated as ``[,].''
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</para>
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</sect1>
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-->
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<sect1>
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<title>More Advanced Features</title>
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@ -150,11 +150,15 @@
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(<ulink url="mailto:t-ishii@sra.co.jp">Tatsuo Ishii</ulink>)</entry>
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</row>
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<row>
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<entry>NetBSD</entry>
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<entry>NetBSD 1.4</entry>
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<entry>arm32</entry>
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<entry>v6.5</entry>
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<entry>1999-04-14</entry>
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<entry>v7.0</entry>
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<entry>2000-04-08</entry>
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<entry>(<ulink url="mailto:prlw1@newn.cam.ac.uk">Patrick
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Welche</ulink>)</entry>
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<!--
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<entry>(<ulink url="mailto:a.mcmurry1@physics.oxford.ac.uk">Andrew McMurry</ulink>)</entry>
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-->
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</row>
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<row>
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<entry>NetBSD 1.4U</entry>
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@ -1,5 +1,5 @@
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<!--
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$Header: /cvsroot/pgsql/doc/src/sgml/query.sgml,v 1.10 2000/04/07 13:30:58 thomas Exp $
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$Header: /cvsroot/pgsql/doc/src/sgml/query.sgml,v 1.11 2000/04/11 05:39:06 thomas Exp $
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-->
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<chapter id="query">
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@ -21,8 +21,8 @@ $Header: /cvsroot/pgsql/doc/src/sgml/query.sgml,v 1.10 2000/04/07 13:30:58 thoma
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flavor of <acronym>SQL</acronym> and is in no way a complete tutorial on
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<acronym>SQL</acronym>. Numerous books have been written on
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<acronym>SQL92</acronym>, including
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<xref linkend="MELT93" endterm="MELT93-title"> and
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<xref linkend="DATE97" endterm="DATE97-title">.
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<xref linkend="MELT93" endterm="MELT93"> and
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<xref linkend="DATE97" endterm="DATE97">.
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You should be aware that some language features
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are extensions to the <acronym>ANSI</acronym> standard.
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</para>
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@ -1,5 +1,5 @@
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<!--
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$Header: /cvsroot/pgsql/doc/src/sgml/ref/comment.sgml,v 1.3 1999/10/26 16:36:28 momjian Exp $
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$Header: /cvsroot/pgsql/doc/src/sgml/ref/comment.sgml,v 1.4 2000/04/11 05:39:15 thomas Exp $
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Postgres documentation
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-->
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@ -101,7 +101,7 @@ COMMENT
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<para>
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<command>COMMENT</command> adds a comment to an object that can be
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easily retrieved with <application>psql's</application>
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<emphasize>\dd</emphasize> command.
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<emphasis>\dd</emphasis> command.
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To remove a comment, use <literal>NULL</literal>.
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Comments are automatically dropped when the object is dropped.
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</para>
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@ -1,5 +1,5 @@
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<!--
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$Header: /cvsroot/pgsql/doc/src/sgml/ref/create_index.sgml,v 1.10 2000/03/16 14:39:30 thomas Exp $
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$Header: /cvsroot/pgsql/doc/src/sgml/ref/create_index.sgml,v 1.11 2000/04/11 05:39:15 thomas Exp $
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Postgres documentation
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-->
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@ -46,8 +46,8 @@ CREATE [ UNIQUE ] INDEX <replaceable class="parameter">index_name</replaceable>
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Causes the system to check for
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duplicate values in the table when the index is created (if data
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already exist) and each time data is added. Attempts to
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insert or update non-duplicate data will generate an
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error.
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insert or update data which would result in duplicate entries
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will generate an error.
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</para>
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</listitem>
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</varlistentry>
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@ -1,5 +1,5 @@
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<!--
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$Header: /cvsroot/pgsql/doc/src/sgml/ref/update.sgml,v 1.8 2000/03/26 18:32:27 petere Exp $
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$Header: /cvsroot/pgsql/doc/src/sgml/ref/update.sgml,v 1.9 2000/04/11 05:39:15 thomas Exp $
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Postgres documentation
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-->
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@ -182,7 +182,7 @@ SELECT * FROM films WHERE kind = 'Dramatic' OR kind = 'Drama';
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the positioned UPDATE statement:
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<synopsis>
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UPDATE table SET column = expression [, ...]
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UPDATE <replaceable>table</replaceable> SET <replaceable>column</replaceable> = <replaceable>expression</replaceable> [, ...]
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WHERE CURRENT OF <replaceable class="parameter">cursor</replaceable>
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</synopsis>
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