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<!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>F.44. tcn — a trigger function to notify listeners of changes to table content</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 Vsnapshot" /><link rel="prev" href="tablefunc.html" title="F.43. tablefunc — functions that return tables (crosstab and others)" /><link rel="next" href="test-decoding.html" title="F.45. test_decoding — SQL-based test/example module for WAL logical decoding" /></head><body id="docContent" class="container-fluid col-10"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">F.44. tcn — a trigger function to notify listeners of changes to table content</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="tablefunc.html" title="F.43. tablefunc — functions that return tables (crosstab and others)">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="contrib.html" title="Appendix F. Additional Supplied Modules and Extensions">Up</a></td><th width="60%" align="center">Appendix F. Additional Supplied Modules and Extensions</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 16.3 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="test-decoding.html" title="F.45. test_decoding — SQL-based test/example module for WAL logical decoding">Next</a></td></tr></table><hr /></div><div class="sect1" id="TCN"><div class="titlepage"><div><div><h2 class="title" style="clear: both">F.44. tcn — a trigger function to notify listeners of changes to table content <a href="#TCN" class="id_link">#</a></h2></div></div></div><a id="id-1.11.7.54.2" class="indexterm"></a><a id="id-1.11.7.54.3" class="indexterm"></a><p>
The <code class="filename">tcn</code> module provides a trigger function that notifies
listeners of changes to any table on which it is attached. It must be
used as an <code class="literal">AFTER</code> trigger <code class="literal">FOR EACH ROW</code>.
</p><p>
This module is considered <span class="quote">“<span class="quote">trusted</span>”</span>, that is, it can be
installed by non-superusers who have <code class="literal">CREATE</code> privilege
on the current database.
</p><p>
Only one parameter may be supplied to the function in a
<code class="literal">CREATE TRIGGER</code> statement, and that is optional. If supplied
it will be used for the channel name for the notifications. If omitted
<code class="literal">tcn</code> will be used for the channel name.
</p><p>
The payload of the notifications consists of the table name, a letter to
indicate which type of operation was performed, and column name/value pairs
for primary key columns. Each part is separated from the next by a comma.
For ease of parsing using regular expressions, table and column names are
always wrapped in double quotes, and data values are always wrapped in
single quotes. Embedded quotes are doubled.
</p><p>
A brief example of using the extension follows.
</p><pre class="programlisting">
test=# create table tcndata
test-# (
test(# a int not null,
test(# b date not null,
test(# c text,
test(# primary key (a, b)
test(# );
CREATE TABLE
test=# create trigger tcndata_tcn_trigger
test-# after insert or update or delete on tcndata
test-# for each row execute function triggered_change_notification();
CREATE TRIGGER
test=# listen tcn;
LISTEN
test=# insert into tcndata values (1, date '2012-12-22', 'one'),
test-# (1, date '2012-12-23', 'another'),
test-# (2, date '2012-12-23', 'two');
INSERT 0 3
Asynchronous notification "tcn" with payload ""tcndata",I,"a"='1',"b"='2012-12-22'" received from server process with PID 22770.
Asynchronous notification "tcn" with payload ""tcndata",I,"a"='1',"b"='2012-12-23'" received from server process with PID 22770.
Asynchronous notification "tcn" with payload ""tcndata",I,"a"='2',"b"='2012-12-23'" received from server process with PID 22770.
test=# update tcndata set c = 'uno' where a = 1;
UPDATE 2
Asynchronous notification "tcn" with payload ""tcndata",U,"a"='1',"b"='2012-12-22'" received from server process with PID 22770.
Asynchronous notification "tcn" with payload ""tcndata",U,"a"='1',"b"='2012-12-23'" received from server process with PID 22770.
test=# delete from tcndata where a = 1 and b = date '2012-12-22';
DELETE 1
Asynchronous notification "tcn" with payload ""tcndata",D,"a"='1',"b"='2012-12-22'" received from server process with PID 22770.
</pre><p>
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