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Bring CREATE RULE reference page into some semblance of agreement with
what's actually implemented.
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‎doc/src/sgml/ref/create_rule.sgml

Lines changed: 81 additions & 154 deletions
Original file line numberDiff line numberDiff line change
@@ -1,5 +1,5 @@
11
<!--
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$Header: /cvsroot/pgsql/doc/src/sgml/ref/create_rule.sgml,v 1.20 2000/12/12 16:47:52 momjian Exp $
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$Header: /cvsroot/pgsql/doc/src/sgml/ref/create_rule.sgml,v 1.21 2001/01/06 04:14:35 tgl Exp $
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Postgres documentation
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-->
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@@ -20,17 +20,27 @@ Postgres documentation
2020
</refnamediv>
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<refsynopsisdiv>
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<refsynopsisdivinfo>
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<date>1999-07-20</date>
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<date>2001-01-05</date>
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</refsynopsisdivinfo>
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<synopsis>
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CREATE RULE <replaceable class="parameter">name</replaceable> AS ON <replaceable class="parameter">event</replaceable>
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TO <replaceable class="parameter">object</replaceable> [ WHERE <replaceable class="parameter">condition</replaceable> ]
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DO [ INSTEAD ] [ <replaceable class="parameter">action</replaceable> | NOTHING ]
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DO [ INSTEAD ] <replaceable class="parameter">action</replaceable>
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where <replaceable class="PARAMETER">action</replaceable> can be:
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NOTHING
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|
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<replaceable class="parameter">query</replaceable>
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|
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( <replaceable class="parameter">query</replaceable> ; <replaceable class="parameter">query</replaceable> ... )
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|
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[ <replaceable class="parameter">query</replaceable> ; <replaceable class="parameter">query</replaceable> ... ]
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</synopsis>
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<refsect2 id="R2-SQL-CREATERULE-1">
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<refsect2info>
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<date>1998-09-11</date>
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<date>2001-01-05</date>
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</refsect2info>
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<title>
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Inputs
@@ -50,9 +60,9 @@ CREATE RULE <replaceable class="parameter">name</replaceable> AS ON <replaceable
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<term><replaceable class="parameter">event</replaceable></term>
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<listitem>
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<para>
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Event is one of <literal>select</literal>,
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<literal>update</literal>, <literal>delete</literal>
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or <literal>insert</literal>.
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Event is one of <literal>SELECT</literal>,
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<literal>UPDATE</literal>, <literal>DELETE</literal>
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or <literal>INSERT</literal>.
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</para>
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</listitem>
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</varlistentry>
@@ -62,32 +72,48 @@ CREATE RULE <replaceable class="parameter">name</replaceable> AS ON <replaceable
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<para>
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Object is either <replaceable class="parameter">table</replaceable>
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or <replaceable class="parameter">table</replaceable>.<replaceable
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class="parameter">column</replaceable>.
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class="parameter">column</replaceable>. (Currently, only the
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<replaceable class="parameter">table</replaceable> form is
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actually implemented.)
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><replaceable class="parameter">condition</replaceable></term>
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<listitem>
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<para>
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Any SQL WHERE clause, <literal>new</literal> or
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<literal>old</literal>, can appear instead of an instance
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variable whenever an instance variable is permissible in SQL.
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Any SQL boolean-condition expression. The condition expression may not
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refer to any tables except <literal>new</literal> and
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<literal>old</literal>.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><replaceable class="parameter">action</replaceable></term>
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<term><replaceable class="parameter">query</replaceable></term>
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<listitem>
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<para>
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Any SQL statement, <literal>new</literal> or
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<literal>old</literal>, can appear instead of an instance
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variable whenever an instance variable is permissible in SQL.
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The query or queries making up the
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<replaceable class="PARAMETER">action</replaceable>
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can be any SQL <literal>SELECT</literal>, <literal>INSERT</literal>,
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<literal>UPDATE</literal>, <literal>DELETE</literal>, or
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<literal>NOTIFY</literal> statement.
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</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</para>
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<para>
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Within the <replaceable class="parameter">condition</replaceable>
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and <replaceable class="PARAMETER">action</replaceable>, the special
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table names <literal>new</literal> and <literal>old</literal> may be
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used to refer to values in the referenced table (the
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<replaceable class="parameter">object</replaceable>).
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<literal>new</literal> is valid in ON INSERT and ON UPDATE rules
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to refer to the new row being inserted or updated.
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<literal>old</literal> is valid in ON SELECT, ON UPDATE, and ON DELETE
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rules to refer to the existing row being selected, updated, or deleted.
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</para>
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</refsect2>
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93119
<refsect2 id="R2-SQL-CREATERULE-2">
@@ -127,26 +153,42 @@ CREATE
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The <productname>Postgres</productname>
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<firstterm>rule system</firstterm> allows one to define an
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alternate action to be performed on inserts, updates, or deletions
130-
from database tables or classes. Currently, rules are used to
131-
implement table views.
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from database tables. Rules are used to
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implement table views as well.
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</para>
133159

134160
<para>
135-
The semantics of a rule is that at the time an individual instance is
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The semantics of a rule is that at the time an individual instance (row)
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is
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accessed, inserted, updated, or deleted, there is an old instance (for
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selects, updates and deletes) and a new instance (for inserts and
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updates).
139-
If the <replaceable class="parameter">event</replaceable>
140-
specified in the ON clause and the
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updates). All the rules for the given event type and the given target
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object (table) are examined, in an unspecified order. If the
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<replaceable class="parameter">condition</replaceable> specified in the
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WHERE clause are true for the old instance, the
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WHERE clause (if any) is true, the
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<replaceable class="parameter">action</replaceable> part of the rule is
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executed. First, however, values from fields in the old instance
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and/or the new instance are substituted for
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executed. The <replaceable class="parameter">action</replaceable> is
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done instead of the original query if INSTEAD is specified; otherwise
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it is done before the original query is performed.
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Within both the <replaceable class="parameter">condition</replaceable>
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and <replaceable class="parameter">action</replaceable>, values from
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fields in the old instance and/or the new instance are substituted for
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<literal>old.</literal><replaceable class="parameter">attribute-name</replaceable>
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and <literal>new.</literal><replaceable class="parameter">attribute-name</replaceable>.
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</para>
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<para>
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The <replaceable class="parameter">action</replaceable> part of the rule
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can consist of one or more queries. To write multiple queries, surround
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them with either parentheses or square brackets. Such queries will be
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performed in the specified order (whereas there are no guarantees about
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the execution order of multiple rules for an object). The
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<replaceable class="parameter">action</replaceable> can also be NOTHING
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indicating no action. Thus, a DO INSTEAD NOTHING rule suppresses the
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original query from executing (when its condition is true); a DO NOTHING
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rule is useless.
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</para>
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<para>
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The <replaceable class="parameter">action</replaceable> part of the rule
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executes with the same command and transaction identifier as the user
@@ -155,47 +197,29 @@ CREATE
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156198
<refsect2 id="R2-SQL-CREATERULE-3">
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<refsect2info>
158-
<date>1998-09-11</date>
200+
<date>2001-01-05</date>
159201
</refsect2info>
160202
<title>
161203
Notes
162204
</title>
163205
<para>
164-
A caution about SQL rules is in order. If the same class name
165-
or instance variable appears in the
166-
<replaceable class="parameter">event</replaceable>,
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<replaceable class="parameter">condition</replaceable> and
168-
<replaceable class="parameter">action</replaceable> parts of a rule,
169-
they are all considered different tuple variables. More accurately,
170-
<literal>new</literal> and <literal>old</literal> are the only tuple
171-
variables that are shared between these clauses. For example, the following
172-
two rules have the same semantics:
173-
<programlisting>
174-
ON UPDATE TO emp.salary WHERE emp.name = "Joe"
175-
DO
176-
UPDATE emp SET ... WHERE ...
177-
</programlisting>
178-
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<programlisting>
180-
ON UPDATE TO emp-1.salary WHERE emp-2.name = "Joe"
181-
DO
182-
UPDATE emp-3 SET ... WHERE ...
183-
</programlisting>
206+
Presently, ON SELECT rules must be unconditional INSTEAD rules and must
207+
have actions that consist of a single SELECT query. Thus, an ON SELECT
208+
rule effectively turns the object table into a view, whose visible
209+
contents are the rows returned by the rule's SELECT query rather than
210+
whatever had been stored in the table (if anything). It is considered
211+
better style to write a CREATE VIEW command than to create a table and
212+
define an ON SELECT rule for it.
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</para>
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185-
Each rule can have the optional tag INSTEAD.
186-
Without
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this tag, <replaceable class="parameter">action</replaceable> will be
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performed in addition to the user command when the
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<replaceable class="parameter">event</replaceable> in the
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<replaceable class="parameter">condition</replaceable> part of the rule
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occurs. Alternately, the
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<replaceable class="parameter">action</replaceable> part will be done
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instead of the user command. In this latter case, the
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<replaceable class="parameter">action</replaceable> can be the keyword
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<literal>NOTHING</literal>.
215+
<para>
216+
You must have rule definition access to a class in order
217+
to define a rule on it. Use <command>GRANT</command>
218+
and <command>REVOKE</command> to change permissions.
196219
</para>
220+
197221
<para>
198-
It is very important to note to avoid circular rules.
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It is very important to take care to avoid circular rules.
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For example, though each
200224
of the following two rule definitions are accepted by
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<productname>Postgres</productname>, the
@@ -226,105 +250,8 @@ SELECT * FROM emp;
226250
</programlisting></para>
227251
</example>
228252
</para>
229-
230-
<para>
231-
You must have rule definition access to a class in order
232-
to define a rule on it. Use <command>GRANT</command>
233-
and <command>REVOKE</command> to change permissions.
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</para>
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236-
<para>
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The object in a <acronym>SQL</acronym> rule cannot be an array reference and
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cannot have parameters.
239-
</para>
240-
241-
<para>
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Aside from the "oid" field, system attributes cannot be
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referenced anywhere in a rule. Among other things, this
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means that functions of instances (e.g., <literal>foo(emp)</literal> where
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<literal>emp</literal> is a class) cannot be called anywhere in a rule.
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</para>
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<para>
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The rule system stores the rule text and query plans as
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text attributes. This implies that creation of rules may
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fail if the rule plus its various internal representations
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exceed some value that is on the order of one page (8KB).
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</para>
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</refsect2>
255254
</refsect1>
256-
257-
<refsect1 id="R1-SQL-CREATERULE-2">
258-
<title>
259-
Usage
260-
</title>
261-
<para>
262-
Make Sam get the same salary adjustment as Joe:
263-
264-
<programlisting>
265-
CREATE RULE example_1 AS
266-
ON UPDATE emp.salary WHERE old.name = "Joe"
267-
DO
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UPDATE emp
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SET salary = new.salary
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WHERE emp.name = "Sam";
271-
</programlisting>
272-
273-
At the time Joe receives a salary adjustment, the event
274-
will become true and Joe's old instance and proposed
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new instance are available to the execution routines.
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Hence, his new salary is substituted into the action part
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of the rule which is subsequently executed. This propagates
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Joe's salary on to Sam.
279-
</para>
280-
<para>
281-
Make Bill get Joe's salary when it is accessed:
282-
<programlisting>
283-
CREATE RULE example_2 AS
284-
ON SELECT TO EMP.salary
285-
WHERE old.name = "Bill"
286-
DO INSTEAD
287-
SELECT emp.salary
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FROM emp
289-
WHERE emp.name = "Joe";
290-
</programlisting>
291-
</para>
292-
<para>
293-
Deny Joe access to the salary of employees in the shoe
294-
department (<function>current_user</function> returns the name of
295-
the current user):
296-
<programlisting>
297-
CREATE RULE example_3 AS
298-
ON
299-
SELECT TO emp.salary
300-
WHERE old.dept = "shoe" AND current_user = "Joe"
301-
DO INSTEAD NOTHING;
302-
</programlisting>
303-
</para>
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<para>
305-
Create a view of the employees working in the toy department:
306-
<programlisting>
307-
CREATE toyemp(name = char16, salary = int4);
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309-
CREATE RULE example_4 AS
310-
ON SELECT TO toyemp
311-
DO INSTEAD
312-
SELECT emp.name, emp.salary
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FROM emp
314-
WHERE emp.dept = "toy";
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</programlisting>
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</para>
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<para>
318-
All new employees must make 5,000 or less:
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<programlisting>
320-
CREATE RULE example_5 AS
321-
ON INERT TO emp WHERE new.salary > 5000
322-
DO
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UPDATE emp SET salary = 5000
324-
WHERE emp.oid = new.oid;
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</programlisting>
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</para>
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</refsect1>
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<refsect1 id="R1-SQL-CREATERULE-4">
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<title>

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