tcn 模块提供一个触发器函数，用于将其所附着的任意表的内容变更通知给监听者。它必须作为 AFTER 触发器，并以 FOR EACH ROW 方式使用。

该模块被认为是“受信任的”，也就是说，它可以由在当前数据库上具有 CREATE 权限的非超级用户安装。

在 CREATE TRIGGER 语句中，至多可以为该函数提供一个参数，而且该参数是可选的。如果提供该参数，它将用作通知的通道名；如果省略，则使用 tcn 作为通道名。

通知的载荷由表名、一个用于指示执行了哪种操作的字母，以及主键列的列名/值对组成。各部分之间都以逗号分隔。为了便于用正则表达式解析，表名和列名始终用双引号括起，数据值始终用单引号括起。嵌入的引号会被双写。

下面给出一个使用该扩展的简短示例。

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.