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Support triggers on views.

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This patch adds the SQL-standard concept of an INSTEAD OF trigger, which
is fired instead of performing a physical insert/update/delete.  The
trigger function is passed the entire old and/or new rows of the view,
and must figure out what to do to the underlying tables to implement
the update.  So this feature can be used to implement updatable views
using trigger programming style rather than rule hacking.

In passing, this patch corrects the names of some columns in the
information_schema.triggers view.  It seems the SQL committee renamed
them somewhere between SQL:99 and SQL:2003.

Dean Rasheed, reviewed by Bernd Helmle; some additional hacking by me.
This commit is contained in:
Tom Lane
2010-10-10 13:43:33 -04:00
parent f7b15b5098
commit 2ec993a7cb
47 changed files with 2815 additions and 759 deletions
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10
doc/src/sgml/ref/create_rule.sgml
View File

@@ -53,7 +53,7 @@ CREATE [ OR REPLACE ] RULE <replaceable class="parameter">name</replaceable> AS
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>
Presently, <literal>ON SELECT</literal> rules must be unconditional
<literal>INSTEAD</literal> rules and must have actions that consist
@@ -73,7 +73,9 @@ CREATE [ OR REPLACE ] RULE <replaceable class="parameter">name</replaceable> AS
sufficient for your purposes) to replace update actions on the view
with appropriate updates on other tables. If you want to support
<command>INSERT RETURNING</> and so on, then be sure to put a suitable
<literal>RETURNING</> clause into each of these rules.
<literal>RETURNING</> clause into each of these rules. Alternatively,
an updatable view can be implemented using <literal>INSTEAD OF</>
triggers (see <xref linkend="sql-createtrigger">).
</para>
<para>
@@ -232,12 +234,12 @@ CREATE [ OR REPLACE ] RULE <replaceable class="parameter">name</replaceable> AS
<programlisting>
CREATE RULE "_RETURN" AS
ON SELECT TO t1
DO INSTEAD
DO INSTEAD
SELECT * FROM t2;
CREATE RULE "_RETURN" AS
ON SELECT TO t2
DO INSTEAD
DO INSTEAD
SELECT * FROM t1;
SELECT * FROM t1;

106
doc/src/sgml/ref/create_trigger.sgml
View File

@@ -21,7 +21,7 @@ PostgreSQL documentation
<refsynopsisdiv>
<synopsis>
CREATE TRIGGER <replaceable class="PARAMETER">name</replaceable> { BEFORE | AFTER } { <replaceable class="PARAMETER">event</replaceable> [ OR ... ] }
CREATE TRIGGER <replaceable class="PARAMETER">name</replaceable> { BEFORE | AFTER | INSTEAD OF } { <replaceable class="PARAMETER">event</replaceable> [ OR ... ] }
ON <replaceable class="PARAMETER">table</replaceable> [ FOR [ EACH ] { ROW | STATEMENT } ]
[ WHEN ( <replaceable class="parameter">condition</replaceable> ) ]
EXECUTE PROCEDURE <replaceable class="PARAMETER">function_name</replaceable> ( <replaceable class="PARAMETER">arguments</replaceable> )
@@ -33,21 +33,22 @@ CREATE TRIGGER <replaceable class="PARAMETER">name</replaceable> { BEFORE | AFTE
<para>
<command>CREATE TRIGGER</command> creates a new trigger. The
trigger will be associated with the specified table and will
trigger will be associated with the specified table or view and will
execute the specified function <replaceable
class="parameter">function_name</replaceable> when certain events occur.
</para>
<para>
The trigger can be specified to fire either before the
The trigger can be specified to fire before the
operation is attempted on a row (before constraints are checked and
the <command>INSERT</command>, <command>UPDATE</command>, or
<command>DELETE</command> is attempted) or after the operation has
<command>DELETE</command> is attempted); or after the operation has
completed (after constraints are checked and the
<command>INSERT</command>, <command>UPDATE</command>, or
<command>DELETE</command> has completed). If the trigger fires
before the event, the trigger can skip the operation for the
current row, or change the row being inserted (for
<command>DELETE</command> has completed); or instead of the operation
(in the case of inserts, updates or deletes on a view).
If the trigger fires before or instead of the event, the trigger can skip
the operation for the current row, or change the row being inserted (for
<command>INSERT</command> and <command>UPDATE</command> operations
only). If the trigger fires after the event, all changes, including
the effects of other triggers, are <quote>visible</quote>
@@ -68,11 +69,71 @@ CREATE TRIGGER <replaceable class="PARAMETER">name</replaceable> { BEFORE | AFTE
</para>
<para>
In addition, triggers may be defined to fire for a
Triggers that are specified to fire <literal>INSTEAD OF</> the trigger
event must be marked <literal>FOR EACH ROW</>, and can only be defined
on views. <literal>BEFORE</> and <literal>AFTER</> triggers on a view
must be marked as <literal>FOR EACH STATEMENT</>.
</para>
<para>
In addition, triggers may be defined to fire for
<command>TRUNCATE</command>, though only
<literal>FOR EACH STATEMENT</literal>.
</para>
<para>
The following table summarizes which types of triggers may be used on
tables and views:
</para>
<informaltable id="supported-trigger-types">
<tgroup cols="4">
<thead>
<row>
<entry>When</entry>
<entry>Event</entry>
<entry>Row-level</entry>
<entry>Statement-level</entry>
</row>
</thead>
<tbody>
<row>
<entry align="center" morerows="1"><literal>BEFORE</></entry>
<entry align="center"><command>INSERT</>/<command>UPDATE</>/<command>DELETE</></entry>
<entry align="center">Tables</entry>
<entry align="center">Tables and views</entry>
</row>
<row>
<entry align="center"><command>TRUNCATE</></entry>
<entry align="center">&mdash;</entry>
<entry align="center">Tables</entry>
</row>
<row>
<entry align="center" morerows="1"><literal>AFTER</></entry>
<entry align="center"><command>INSERT</>/<command>UPDATE</>/<command>DELETE</></entry>
<entry align="center">Tables</entry>
<entry align="center">Tables and views</entry>
</row>
<row>
<entry align="center"><command>TRUNCATE</></entry>
<entry align="center">&mdash;</entry>
<entry align="center">Tables</entry>
</row>
<row>
<entry align="center" morerows="1"><literal>INSTEAD OF</></entry>
<entry align="center"><command>INSERT</>/<command>UPDATE</>/<command>DELETE</></entry>
<entry align="center">Views</entry>
<entry align="center">&mdash;</entry>
</row>
<row>
<entry align="center"><command>TRUNCATE</></entry>
<entry align="center">&mdash;</entry>
<entry align="center">&mdash;</entry>
</row>
</tbody>
</tgroup>
</informaltable>
<para>
Also, a trigger definition can specify a Boolean <literal>WHEN</>
condition, which will be tested to see whether the trigger should
@@ -116,10 +177,11 @@ CREATE TRIGGER <replaceable class="PARAMETER">name</replaceable> { BEFORE | AFTE
<varlistentry>
<term><literal>BEFORE</literal></term>
<term><literal>AFTER</literal></term>
<term><literal>INSTEAD OF</literal></term>
<listitem>
<para>
Determines whether the function is called before or after the
event.
Determines whether the function is called before, after, or instead of
the event.
</para>
</listitem>
</varlistentry>
@@ -143,6 +205,10 @@ UPDATE OF <replaceable>column_name1</replaceable> [, <replaceable>column_name2</
The trigger will only fire if at least one of the listed columns
is mentioned as a target of the update.
</para>
<para>
<literal>UPDATE INSTEAD OF</> triggers do not support lists of columns.
</para>
</listitem>
</varlistentry>
@@ -150,7 +216,7 @@ UPDATE OF <replaceable>column_name1</replaceable> [, <replaceable>column_name2</
<term><replaceable class="parameter">table</replaceable></term>
<listitem>
<para>
The name (optionally schema-qualified) of the table the trigger
The name (optionally schema-qualified) of the table or view the trigger
is for.
</para>
</listitem>
@@ -188,6 +254,11 @@ UPDATE OF <replaceable>column_name1</replaceable> [, <replaceable>column_name2</
and <literal>DELETE</> triggers cannot refer to <literal>NEW</>.
</para>
<para>
<literal>INSTEAD OF</> triggers do not support <literal>WHEN</>
conditions.
</para>
<para>
Currently, <literal>WHEN</literal> expressions cannot contain
subqueries.
@@ -326,6 +397,16 @@ CREATE TRIGGER log_update
WHEN (OLD.* IS DISTINCT FROM NEW.*)
EXECUTE PROCEDURE log_account_update();
</programlisting>
Execute the function <function>view_insert_row</> for each row to insert
rows into the tables underlying a view:
<programlisting>
CREATE TRIGGER view_insert
INSTEAD OF INSERT ON my_view
FOR EACH ROW
EXECUTE PROCEDURE view_insert_row();
</programlisting>
</para>
<para>
@@ -396,7 +477,8 @@ CREATE TRIGGER log_update
<para>
The ability to fire triggers for <command>TRUNCATE</command> is a
<productname>PostgreSQL</> extension of the SQL standard.
<productname>PostgreSQL</> extension of the SQL standard, as is the
ability to define statement-level triggers on views.
</para>
</refsect1>