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<!--
doc/src/sgml/ref/create_event_trigger.sgml
PostgreSQL documentation
-->
<refentry id="SQL-CREATEEVENTTRIGGER">
<refmeta>
<refentrytitle>CREATE EVENT TRIGGER</refentrytitle>
<manvolnum>7</manvolnum>
<refmiscinfo>SQL - Language Statements</refmiscinfo>
</refmeta>
<refnamediv>
<refname>CREATE EVENT TRIGGER</refname>
<refpurpose>define a new event trigger</refpurpose>
</refnamediv>
<indexterm zone="sql-createeventtrigger">
<primary>CREATE EVENT TRIGGER</primary>
</indexterm>
<refsynopsisdiv>
<synopsis>
CREATE EVENT TRIGGER <replaceable class="PARAMETER">name</replaceable>
ON <replaceable class="PARAMETER">event</replaceable>
[ WHEN <replaceable class="PARAMETER">filter_variable</replaceable> IN (filter_value [ AND ... ] ) ]
EXECUTE PROCEDURE <replaceable class="PARAMETER">function_name</replaceable>()
</synopsis>
</refsynopsisdiv>
<refsect1>
<title>Description</title>
<para>
<command>CREATE EVENT TRIGGER</command> creates a new event trigger.
Whenever the designated event occurs and the <literal>WHEN</> condition
associated with the trigger, if any, is satisfied, the trigger function
will be executed. For a general introduction to event triggers, see
<xref linkend="event-triggers">. The user who creates an event trigger
becomes its owner.
</para>
</refsect1>
<refsect1>
<title>Parameters</title>
<variablelist>
<varlistentry>
<term><replaceable class="parameter">name</replaceable></term>
<listitem>
<para>
The name to give the new trigger. This name must be unique within
the database.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable class="parameter">event</replaceable></term>
<listitem>
<para>
The name of the event that triggers a call to the given function.
See <xref linkend="event-trigger-definition"> for more information
on event names.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable class="parameter">filter_variable</replaceable></term>
<listitem>
<para>
The name of a variable used to filter events. This makes it possible
to restrict the firing of the trigger to a subset of the cases in which
it is supported. Currently the only supported
<replaceable class="parameter">filter_variable</replaceable>
is <literal>TAG</literal>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable class="parameter">filter_value</replaceable></term>
<listitem>
<para>
A list of values for the
associated <replaceable class="parameter">filter_variable</replaceable>
for which the trigger should fire. For <literal>TAG</>, this means a
list of command tags (e.g. <literal>'DROP FUNCTION'</>).
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable class="parameter">function_name</replaceable></term>
<listitem>
<para>
A user-supplied function that is declared as taking no argument and
returning type <literal>event_trigger</literal>.
</para>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1 id="sql-createeventtrigger-notes">
<title>Notes</title>
<para>
To create a trigger on a event, the user must be superuser.
</para>
</refsect1>
<refsect1 id="sql-createeventtrigger-examples">
<title>Examples</title>
<para>
Forbid the execution of any <link linkend="ddl">ddl</link> command:
<programlisting>
CREATE OR REPLACE FUNCTION abort_any_command()
RETURNS event_trigger
LANGUAGE plpgsql
AS $$
BEGIN
RAISE EXCEPTION 'command % is disabled', tg_tag;
END;
$$;
CREATE EVENT TRIGGER abort_ddl ON ddl_command_start
EXECUTE PROCEDURE abort_any_command();
</programlisting>
</para>
</refsect1>
<refsect1 id="sql-createeventtrigger-compatibility">
<title>Compatibility</title>
<para>
There is no <command>CREATE EVENT TRIGGER</command> statement in the
SQL standard.
</para>
</refsect1>
<refsect1>
<title>See Also</title>
<simplelist type="inline">
<member><xref linkend="sql-createfunction"></member>
<member><xref linkend="sql-altereventtrigger"></member>
<member><xref linkend="sql-dropeventtrigger"></member>
</simplelist>
</refsect1>
</refentry>
|
