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func.sgml has grown over the years to the point where it is very difficult to manage. This commit splits out each sect1 piece into its own file, which is then included in the main file, so that the built documentation should be identical to the pre-split documentation. All these new files are placed in a new "func" subdirectory, and the previous func.sgml is removed. Done using scripts developed by: Author: jian he <jian.universality@gmail.com> Discussion: https://postgr.es/m/CACJufxFgAh1--EMwOjMuANe=VTmjkNaZjH+AzSe04-8ZCGiESA@mail.gmail.com
333 lines
10 KiB
Plaintext
333 lines
10 KiB
Plaintext
<sect1 id="functions-event-triggers">
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<title>Event Trigger Functions</title>
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<para>
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<productname>PostgreSQL</productname> provides these helper functions
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to retrieve information from event triggers.
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</para>
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<para>
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For more information about event triggers,
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see <xref linkend="event-triggers"/>.
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</para>
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<sect2 id="pg-event-trigger-ddl-command-end-functions">
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<title>Capturing Changes at Command End</title>
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<indexterm>
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<primary>pg_event_trigger_ddl_commands</primary>
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</indexterm>
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<synopsis>
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<function>pg_event_trigger_ddl_commands</function> () <returnvalue>setof record</returnvalue>
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</synopsis>
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<para>
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<function>pg_event_trigger_ddl_commands</function> returns a list of
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<acronym>DDL</acronym> commands executed by each user action,
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when invoked in a function attached to a
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<literal>ddl_command_end</literal> event trigger. If called in any other
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context, an error is raised.
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<function>pg_event_trigger_ddl_commands</function> returns one row for each
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base command executed; some commands that are a single SQL sentence
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may return more than one row. This function returns the following
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columns:
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<informaltable>
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<tgroup cols="3">
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<thead>
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<row>
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<entry>Name</entry>
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<entry>Type</entry>
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<entry>Description</entry>
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</row>
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</thead>
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<tbody>
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<row>
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<entry><literal>classid</literal></entry>
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<entry><type>oid</type></entry>
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<entry>OID of catalog the object belongs in</entry>
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</row>
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<row>
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<entry><literal>objid</literal></entry>
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<entry><type>oid</type></entry>
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<entry>OID of the object itself</entry>
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</row>
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<row>
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<entry><literal>objsubid</literal></entry>
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<entry><type>integer</type></entry>
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<entry>Sub-object ID (e.g., attribute number for a column)</entry>
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</row>
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<row>
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<entry><literal>command_tag</literal></entry>
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<entry><type>text</type></entry>
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<entry>Command tag</entry>
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</row>
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<row>
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<entry><literal>object_type</literal></entry>
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<entry><type>text</type></entry>
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<entry>Type of the object</entry>
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</row>
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<row>
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<entry><literal>schema_name</literal></entry>
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<entry><type>text</type></entry>
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<entry>
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Name of the schema the object belongs in, if any; otherwise <literal>NULL</literal>.
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No quoting is applied.
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</entry>
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</row>
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<row>
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<entry><literal>object_identity</literal></entry>
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<entry><type>text</type></entry>
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<entry>
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Text rendering of the object identity, schema-qualified. Each
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identifier included in the identity is quoted if necessary.
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</entry>
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</row>
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<row>
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<entry><literal>in_extension</literal></entry>
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<entry><type>boolean</type></entry>
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<entry>True if the command is part of an extension script</entry>
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</row>
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<row>
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<entry><literal>command</literal></entry>
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<entry><type>pg_ddl_command</type></entry>
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<entry>
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A complete representation of the command, in internal format.
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This cannot be output directly, but it can be passed to other
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functions to obtain different pieces of information about the
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command.
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</entry>
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</row>
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</tbody>
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</tgroup>
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</informaltable>
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</para>
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</sect2>
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<sect2 id="pg-event-trigger-sql-drop-functions">
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<title>Processing Objects Dropped by a DDL Command</title>
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<indexterm>
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<primary>pg_event_trigger_dropped_objects</primary>
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</indexterm>
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<synopsis>
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<function>pg_event_trigger_dropped_objects</function> () <returnvalue>setof record</returnvalue>
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</synopsis>
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<para>
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<function>pg_event_trigger_dropped_objects</function> returns a list of all objects
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dropped by the command in whose <literal>sql_drop</literal> event it is called.
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If called in any other context, an error is raised.
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This function returns the following columns:
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<informaltable>
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<tgroup cols="3">
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<thead>
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<row>
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<entry>Name</entry>
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<entry>Type</entry>
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<entry>Description</entry>
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</row>
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</thead>
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<tbody>
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<row>
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<entry><literal>classid</literal></entry>
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<entry><type>oid</type></entry>
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<entry>OID of catalog the object belonged in</entry>
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</row>
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<row>
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<entry><literal>objid</literal></entry>
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<entry><type>oid</type></entry>
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<entry>OID of the object itself</entry>
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</row>
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<row>
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<entry><literal>objsubid</literal></entry>
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<entry><type>integer</type></entry>
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<entry>Sub-object ID (e.g., attribute number for a column)</entry>
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</row>
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<row>
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<entry><literal>original</literal></entry>
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<entry><type>boolean</type></entry>
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<entry>True if this was one of the root object(s) of the deletion</entry>
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</row>
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<row>
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<entry><literal>normal</literal></entry>
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<entry><type>boolean</type></entry>
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<entry>
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True if there was a normal dependency relationship
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in the dependency graph leading to this object
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</entry>
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</row>
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<row>
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<entry><literal>is_temporary</literal></entry>
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<entry><type>boolean</type></entry>
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<entry>
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True if this was a temporary object
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</entry>
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</row>
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<row>
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<entry><literal>object_type</literal></entry>
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<entry><type>text</type></entry>
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<entry>Type of the object</entry>
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</row>
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<row>
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<entry><literal>schema_name</literal></entry>
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<entry><type>text</type></entry>
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<entry>
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Name of the schema the object belonged in, if any; otherwise <literal>NULL</literal>.
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No quoting is applied.
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</entry>
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</row>
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<row>
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<entry><literal>object_name</literal></entry>
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<entry><type>text</type></entry>
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<entry>
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Name of the object, if the combination of schema and name can be
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used as a unique identifier for the object; otherwise <literal>NULL</literal>.
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No quoting is applied, and name is never schema-qualified.
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</entry>
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</row>
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<row>
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<entry><literal>object_identity</literal></entry>
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<entry><type>text</type></entry>
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<entry>
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Text rendering of the object identity, schema-qualified. Each
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identifier included in the identity is quoted if necessary.
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</entry>
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</row>
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<row>
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<entry><literal>address_names</literal></entry>
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<entry><type>text[]</type></entry>
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<entry>
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An array that, together with <literal>object_type</literal> and
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<literal>address_args</literal>, can be used by
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the <function>pg_get_object_address</function> function to
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recreate the object address in a remote server containing an
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identically named object of the same kind.
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</entry>
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</row>
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<row>
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<entry><literal>address_args</literal></entry>
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<entry><type>text[]</type></entry>
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<entry>
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Complement for <literal>address_names</literal>
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</entry>
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</row>
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</tbody>
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</tgroup>
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</informaltable>
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</para>
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<para>
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The <function>pg_event_trigger_dropped_objects</function> function can be used
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in an event trigger like this:
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<programlisting>
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CREATE FUNCTION test_event_trigger_for_drops()
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RETURNS event_trigger LANGUAGE plpgsql AS $$
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DECLARE
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obj record;
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BEGIN
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FOR obj IN SELECT * FROM pg_event_trigger_dropped_objects()
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LOOP
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RAISE NOTICE '% dropped object: % %.% %',
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tg_tag,
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obj.object_type,
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obj.schema_name,
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obj.object_name,
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obj.object_identity;
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END LOOP;
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END;
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$$;
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CREATE EVENT TRIGGER test_event_trigger_for_drops
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ON sql_drop
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EXECUTE FUNCTION test_event_trigger_for_drops();
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</programlisting>
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</para>
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</sect2>
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<sect2 id="pg-event-trigger-table-rewrite-functions">
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<title>Handling a Table Rewrite Event</title>
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<para>
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The functions shown in
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<xref linkend="functions-event-trigger-table-rewrite"/>
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provide information about a table for which a
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<literal>table_rewrite</literal> event has just been called.
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If called in any other context, an error is raised.
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</para>
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<table id="functions-event-trigger-table-rewrite">
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<title>Table Rewrite Information Functions</title>
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<tgroup cols="1">
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<thead>
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<row>
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<entry role="func_table_entry"><para role="func_signature">
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Function
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</para>
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<para>
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Description
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</para></entry>
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</row>
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</thead>
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<tbody>
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<row>
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<entry role="func_table_entry"><para role="func_signature">
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<indexterm>
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<primary>pg_event_trigger_table_rewrite_oid</primary>
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</indexterm>
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<function>pg_event_trigger_table_rewrite_oid</function> ()
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<returnvalue>oid</returnvalue>
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</para>
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<para>
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Returns the OID of the table about to be rewritten.
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</para></entry>
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</row>
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<row>
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<entry role="func_table_entry"><para role="func_signature">
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<indexterm>
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<primary>pg_event_trigger_table_rewrite_reason</primary>
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</indexterm>
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<function>pg_event_trigger_table_rewrite_reason</function> ()
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<returnvalue>integer</returnvalue>
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</para>
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<para>
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Returns a code explaining the reason(s) for rewriting. The value is
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a bitmap built from the following values: <literal>1</literal>
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(the table has changed its persistence), <literal>2</literal>
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(default value of a column has changed), <literal>4</literal>
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(a column has a new data type) and <literal>8</literal>
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(the table access method has changed).
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</para></entry>
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</row>
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</tbody>
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</tgroup>
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</table>
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<para>
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These functions can be used in an event trigger like this:
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<programlisting>
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CREATE FUNCTION test_event_trigger_table_rewrite_oid()
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RETURNS event_trigger
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LANGUAGE plpgsql AS
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$$
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BEGIN
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RAISE NOTICE 'rewriting table % for reason %',
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pg_event_trigger_table_rewrite_oid()::regclass,
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pg_event_trigger_table_rewrite_reason();
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END;
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$$;
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CREATE EVENT TRIGGER test_table_rewrite_oid
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ON table_rewrite
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EXECUTE FUNCTION test_event_trigger_table_rewrite_oid();
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</programlisting>
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</para>
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</sect2>
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</sect1>
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