tcn 模块提供了一个触发器函数，用于通知监听器附加到其上的任何表的更改。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，非超级用户在当前数据库上具有 CREATE 权限时可以安装它。

在 CREATE TRIGGER 语句中只能向函数提供一个参数，并且该参数是可选的。如果提供，它将用于通知的通道名称。如果省略，则 tcn 将用于通道名称。

通知的有效负载包括表名、指示执行的操作类型的字母以及主键列的列名/值对。每个部分都用逗号与下一个部分分隔。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，数据值始终用单引号括起来。嵌入的引号加倍。

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.