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diff --git a/doc/src/sgml/html/event-trigger-definition.html b/doc/src/sgml/html/event-trigger-definition.html new file mode 100644 index 0000000..2993ab6 --- /dev/null +++ b/doc/src/sgml/html/event-trigger-definition.html @@ -0,0 +1,78 @@ +<?xml version="1.0" encoding="UTF-8" standalone="no"?> +<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>39.1. Overview of Event Trigger Behavior</title><link rel="stylesheet" type="text/css" href="stylesheet.css" /><link rev="made" href="pgsql-docs@lists.postgresql.org" /><meta name="generator" content="DocBook XSL Stylesheets V1.79.1" /><link rel="prev" href="event-triggers.html" title="Chapter 39. Event Triggers" /><link rel="next" href="event-trigger-matrix.html" title="39.2. Event Trigger Firing Matrix" /></head><body id="docContent" class="container-fluid col-10"><div xmlns="http://www.w3.org/TR/xhtml1/transitional" class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">39.1. Overview of Event Trigger Behavior</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="event-triggers.html" title="Chapter 39. Event Triggers">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="event-triggers.html" title="Chapter 39. Event Triggers">Up</a></td><th width="60%" align="center">Chapter 39. Event Triggers</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 13.4 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="event-trigger-matrix.html" title="39.2. Event Trigger Firing Matrix">Next</a></td></tr></table><hr></hr></div><div class="sect1" id="EVENT-TRIGGER-DEFINITION"><div class="titlepage"><div><div><h2 class="title" style="clear: both">39.1. Overview of Event Trigger Behavior</h2></div></div></div><p> + An event trigger fires whenever the event with which it is associated + occurs in the database in which it is defined. Currently, the only + supported events are + <code class="literal">ddl_command_start</code>, + <code class="literal">ddl_command_end</code>, + <code class="literal">table_rewrite</code> + and <code class="literal">sql_drop</code>. + Support for additional events may be added in future releases. + </p><p> + The <code class="literal">ddl_command_start</code> event occurs just before the + execution of a <code class="literal">CREATE</code>, <code class="literal">ALTER</code>, <code class="literal">DROP</code>, + <code class="literal">SECURITY LABEL</code>, + <code class="literal">COMMENT</code>, <code class="literal">GRANT</code> or <code class="literal">REVOKE</code> + command. No check whether the affected object exists or doesn't exist is + performed before the event trigger fires. + As an exception, however, this event does not occur for + DDL commands targeting shared objects — databases, roles, and tablespaces + — or for commands targeting event triggers themselves. The event trigger + mechanism does not support these object types. + <code class="literal">ddl_command_start</code> also occurs just before the execution of a + <code class="literal">SELECT INTO</code> command, since this is equivalent to + <code class="literal">CREATE TABLE AS</code>. + </p><p> + The <code class="literal">ddl_command_end</code> event occurs just after the execution of + this same set of commands. To obtain more details on the <acronym class="acronym">DDL</acronym> + operations that took place, use the set-returning function + <code class="literal">pg_event_trigger_ddl_commands()</code> from the + <code class="literal">ddl_command_end</code> event trigger code (see + <a class="xref" href="functions-event-triggers.html" title="9.29. Event Trigger Functions">Section 9.29</a>). Note that the trigger fires + after the actions have taken place (but before the transaction commits), + and thus the system catalogs can be read as already changed. + </p><p> + The <code class="literal">sql_drop</code> event occurs just before the + <code class="literal">ddl_command_end</code> event trigger for any operation that drops + database objects. To list the objects that have been dropped, use the + set-returning function <code class="literal">pg_event_trigger_dropped_objects()</code> from the + <code class="literal">sql_drop</code> event trigger code (see + <a class="xref" href="functions-event-triggers.html" title="9.29. Event Trigger Functions">Section 9.29</a>). Note that + the trigger is executed after the objects have been deleted from the + system catalogs, so it's not possible to look them up anymore. + </p><p> + The <code class="literal">table_rewrite</code> event occurs just before a table is + rewritten by some actions of the commands <code class="literal">ALTER TABLE</code> and + <code class="literal">ALTER TYPE</code>. While other + control statements are available to rewrite a table, + like <code class="literal">CLUSTER</code> and <code class="literal">VACUUM</code>, + the <code class="literal">table_rewrite</code> event is not triggered by them. + </p><p> + Event triggers (like other functions) cannot be executed in an aborted + transaction. Thus, if a DDL command fails with an error, any associated + <code class="literal">ddl_command_end</code> triggers will not be executed. Conversely, + if a <code class="literal">ddl_command_start</code> trigger fails with an error, no + further event triggers will fire, and no attempt will be made to execute + the command itself. Similarly, if a <code class="literal">ddl_command_end</code> trigger + fails with an error, the effects of the DDL statement will be rolled + back, just as they would be in any other case where the containing + transaction aborts. + </p><p> + For a complete list of commands supported by the event trigger mechanism, + see <a class="xref" href="event-trigger-matrix.html" title="39.2. Event Trigger Firing Matrix">Section 39.2</a>. + </p><p> + Event triggers are created using the command <a class="xref" href="sql-createeventtrigger.html" title="CREATE EVENT TRIGGER"><span class="refentrytitle">CREATE EVENT TRIGGER</span></a>. + In order to create an event trigger, you must first create a function with + the special return type <code class="literal">event_trigger</code>. This function + need not (and may not) return a value; the return type serves merely as + a signal that the function is to be invoked as an event trigger. + </p><p> + If more than one event trigger is defined for a particular event, they will + fire in alphabetical order by trigger name. + </p><p> + A trigger definition can also specify a <code class="literal">WHEN</code> + condition so that, for example, a <code class="literal">ddl_command_start</code> + trigger can be fired only for particular commands which the user wishes + to intercept. A common use of such triggers is to restrict the range of + DDL operations which users may perform. + </p></div><div xmlns="http://www.w3.org/TR/xhtml1/transitional" class="navfooter"><hr></hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="event-triggers.html" title="Chapter 39. 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