tcn 模块提供一个触发器函数，用于向监听者通知其所在表发生的任何变更。它必须用作 AFTER 触发器，且为 FOR EACH ROW 形式。

该模块被视为“可信”模块，也就是说，拥有当前数据库 CREATE 权限的非超级用户也可以安装它。

在 CREATE TRIGGER 语句中，最多只能向该函数提供一个参数，且该参数是可选的。如果提供了该参数，它将用作通知的频道名称；如果省略，则使用 tcn 作为频道名称。

通知的载荷由表名、一个表示所执行操作类型的字母，以及主键列的列名/值对组成。各部分之间以逗号分隔。为便于使用正则表达式解析，表名与列名总是用双引号包裹，数据值总是用单引号包裹。内嵌的引号会被双写。

下面是使用该扩展的简要示例。

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.