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Better document INSTEAD behavior for rules.

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This commit is contained in:
Bruce Momjian 2004-03-04 14:32:12 +00:00
parent f3c6d592d2
commit f503b6a821
1 changed files with 21 additions and 10 deletions
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31
doc/src/sgml/ref/create_rule.sgml
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@ -1,5 +1,5 @@
<!--
$PostgreSQL: pgsql/doc/src/sgml/ref/create_rule.sgml,v 1.42 2003/11/29 19:51:38 pgsql Exp $
$PostgreSQL: pgsql/doc/src/sgml/ref/create_rule.sgml,v 1.43 2004/03/04 14:32:12 momjian Exp $
PostgreSQL documentation
-->
@ -42,15 +42,15 @@ CREATE [ OR REPLACE ] RULE <replaceable class="parameter">name</replaceable> AS
define an alternate action to be performed on insertions, updates,
or deletions in database tables. Roughly speaking, a rule causes
additional commands to be executed when a given command on a given
table is executed. Alternatively, a rule can replace a given
command by another, or cause a command not to be executed at all.
Rules are used to implement table views as well. It is important
to realize that a rule is really a command transformation
mechanism, or command macro. The transformation happens before the
execution of the commands starts. If you actually want an
operation that fires independently for each physical row, you
probably want to use a trigger, not a rule. More information about
the rules system is in <xref linkend="rules">.
table is executed. Alternatively, an <literal>INSTEAD</literal>
rule can replace a given command by another, or cause a command
not to be executed at all. Rules are used to implement table
views as well. It is important to realize that a rule is really
a command transformation mechanism, or command macro. The
transformation happens before the execution of the commands starts.
If you actually want an operation that fires independently for each
physical row, you probably want to use a trigger, not a rule.
More information about the rules system is in <xref linkend="rules">.
</para>
<para>
@ -140,6 +140,17 @@ CREATE [ OR REPLACE ] RULE <replaceable class="parameter">name</replaceable> AS
</listitem>
</varlistentry>
<varlistentry>
<term><option>INSTEAD</option></term>
<listitem>
<para>
<literal>INSTEAD</literal> indicates that the commands should be
executed <emphasis>instead</> of the original command, not in
addition to the original command.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable class="parameter">command</replaceable></term>
<listitem>