Postgresql 中文操作指南
F.44. tcn — a trigger function to notify listeners of changes to table content #
tcn 模块提供了一个触发器函数，用于向侦听器通知其所连接的任何表的变化。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，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，它将被用作通知的通道名称。如果省略，tcn 将被用作通道名称。
通知的有效负载包括表名、指示执行了哪种类型操作的字母，以及主键列的列名/值对。每个部分由逗号分隔。为了使用正则表达式轻松进行解析，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。嵌入的引号加倍。
以下是使用此扩展名的一个简要示例。
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.