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Add some notes about conditional rules used with views.

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Tom Lane 2001-11-06 23:54:32 +00:00
parent f688c1e064
commit 4a3bf197eb
2 changed files with 47 additions and 9 deletions
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46
doc/src/sgml/ref/create_rule.sgml
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@ -1,5 +1,5 @@
<!--
$Header: /cvsroot/pgsql/doc/src/sgml/ref/create_rule.sgml,v 1.28 2001/10/09 18:46:00 petere Exp $
$Header: /cvsroot/pgsql/doc/src/sgml/ref/create_rule.sgml,v 1.29 2001/11/06 23:54:32 tgl Exp $
Postgres documentation
-->
@ -196,10 +196,10 @@ CREATE
<refsect2 id="R2-SQL-CREATERULE-3">
<refsect2info>
<date>2001-01-05</date>
<date>2001-11-06</date>
</refsect2info>
<title>
Notes
Rules and Views
</title>
<para>
Presently, ON SELECT rules must be unconditional INSTEAD rules and must
@ -207,10 +207,44 @@ CREATE
rule effectively turns the object table into a view, whose visible
contents are the rows returned by the rule's SELECT query rather than
whatever had been stored in the table (if anything). It is considered
better style to write a CREATE VIEW command than to create a table and
define an ON SELECT rule for it.
better style to write a CREATE VIEW command than to create a real table
and define an ON SELECT rule for it.
</para>
<para>
<xref linkend="sql-createview"> creates a dummy table (with no underlying
storage) and associates an ON SELECT rule with it. The system will not
allow updates to the view, since it knows there is no real table there.
You can create the
illusion of an updatable view by defining ON INSERT, ON UPDATE, and
ON DELETE rules (or any subset of those that's sufficient
for your purposes) to replace update actions on the view with
appropriate updates on other tables.
</para>
<para>
There is a catch if you try to use conditional
rules for view updates: there <emphasis>must</> be an unconditional
INSTEAD rule for each action you wish to allow on the view. If the
rule is conditional, or is not INSTEAD, then the system will still reject
attempts to perform the update action, because it thinks it might end up
trying to perform the action on the dummy table in some cases.
If you want to
handle all the useful cases in conditional rules, you can; just add an
unconditional DO INSTEAD NOTHING rule to ensure that the system
understands it will never be called on to update the dummy table. Then
make the conditional rules non-INSTEAD; in the cases where they fire,
they add to the default INSTEAD NOTHING action.
</para>
</refsect2>
<refsect2 id="R2-SQL-CREATERULE-4">
<refsect2info>
<date>2001-01-05</date>
</refsect2info>
<title>
Notes
</title>
<para>
You must have rule definition access to a table in order
to define a rule on it. Use <command>GRANT</command>
@ -267,7 +301,7 @@ UPDATE mytable SET name = 'foo' WHERE id = 42;
Compatibility
</title>
<refsect2 id="R2-SQL-CREATERULE-4">
<refsect2 id="R2-SQL-CREATERULE-5">
<refsect2info>
<date>1998-09-11</date>
</refsect2info>

10
doc/src/sgml/ref/create_view.sgml
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@ -1,5 +1,5 @@
<!--
$Header: /cvsroot/pgsql/doc/src/sgml/ref/create_view.sgml,v 1.12 2001/09/03 12:57:49 petere Exp $
$Header: /cvsroot/pgsql/doc/src/sgml/ref/create_view.sgml,v 1.13 2001/11/06 23:54:32 tgl Exp $
Postgres documentation
-->
@ -102,7 +102,7 @@ ERROR: Relation '<replaceable class="parameter">view</replaceable>' already exi
</varlistentry>
<varlistentry>
<term><computeroutput>
NOTICE create: attribute named "<replaceable class="parameter">column</replaceable>" has an unknown type
NOTICE: Attribute '<replaceable class="parameter">column</replaceable>' has an unknown type
</computeroutput></term>
<listitem>
<para>
@ -149,7 +149,11 @@ CREATE VIEW vista AS SELECT text 'Hello World'
</title>
<para>
Currently, views are read only.
Currently, views are read only: the system will not allow an insert,
update, or delete on a view. You can get the effect of an updatable
view by creating rules that rewrite inserts, etc. on the view into
appropriate actions on other tables. For more information see
<xref linkend="sql-createrule">.
</para>
<para>