tcn 模块提供了一个触发函数，用于通知监听器对其附加的任何表的更改。它必须用作AFTER触发器FOR EACH ROW。

此模块被认为是 “受信任的”，也就是说，具有当前数据库CREATE权限的非超级用户可以安装它。

在 CREATE TRIGGER 语句中，该函数只能提供一个参数，并且是可选的。如果提供，它将用作通知的通道名称。如果省略，则tcn将用作通道名称。

通知的有效负载包括表名、一个字母指示执行的操作类型以及主键列的列名/值对。每个部分都用逗号分隔。为了便于使用正则表达式进行解析，表名和列名始终用双引号括起来，而数据值始终用单引号括起来。嵌入的引号会加倍。

下面是一个使用扩展的简短示例。

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.